Expression profile of skin papillomas with high cancer risk displays a unique genetic signature that clusters with squamous cell carcinomas and predicts risk for malignant conversion.

Chemical induction of squamous tumors in the mouse skin induces multiple benign papillomas: high-frequency terminally benign low-risk papillomas and low-frequency high-risk papillomas, the putative precursor lesions to squamous cell carcinoma (SCC). We have compared the gene expression profile of twenty different early low- and high-risk papillomas with normal skin and SCC. Unsupervised clustering of 514 differentially expressed genes (P<0.001) showed that 9/10 high-risk papillomas clustered with SCC, while 1/10 clustered with low-risk papillomas, and this correlated with keratin markers of tumor progression. Prediction analysis for microarrays (PAM) identified 87 genes that distinguished the two papilloma classes, and a majority of these had a similar expression pattern in both high-risk papillomas and SCC. Additional classifier algorithms generated a gene list that correctly classified unknown benign tumors as low- or high-risk concordant with promotion protocol and keratin profiling. Reduced expression of immune function genes characterized the high-risk papillomas and SCC. Immunohistochemistry confirmed reduced T-cell number in high-risk papillomas, suggesting that reduced adaptive immunity defines papillomas that progress to SCC. These results demonstrate that murine premalignant lesions can be segregated into subgroups by gene expression patterns that correlate with risk for malignant conversion, and suggest a paradigm for generating diagnostic biomarkers for human premalignant lesions with unknown individual risk for malignant conversion.

Reactive oxygen species mediate N-(4-hydroxyphenyl)retinamide-induced cell death in malignant T cells and are inhibited by the HTLV-I oncoprotein Tax.

N-(4-hydroxyphenyl)retinamide (HPR) is a synthetic retinoid that inhibits growth of many human tumor cells, including those resistant to natural retinoids. HPR is an effective chemopreventive agent for prostate, cervix, breast, bladder, skin and lung cancers, and has shown promise for the treatment of neuroblastomas. We have previously shown that HPR inhibits proliferation and induces apoptosis of human T-cell lymphotropic virus type I (HTLV-I)-associated adult T-cell leukemia (ATL) and HTLV-I-negative malignant T cells, whereas no effect is observed on normal lymphocytes. In this report, we identified HPR-induced reactive oxygen species (ROS) generation as the key mediator of cell cycle arrest and apoptosis of malignant T cells. HPR treatment of HTLV-I-negative malignant T cells was associated with a rapid and progressive ROS accumulation. Pre-treatment with the antioxidants vitamin C and dithiothreitol inhibited ROS generation, prevented HPR-induced ceramide accumulation, cell cycle arrest, cytochrome c release, caspase-activation and apoptosis. Therefore, anti-oxidants protected malignant T cells from HPR-induced growth inhibition. The expression of the HTLV-I oncoprotein Tax abrogated HPR-induced ROS accumulation in HTLV-I-infected cells, which explains their lower sensitivity to HPR. Defining the mechanism of free radical induction by HPR may support a potential therapeutic role for this synthetic retinoid in ATL and HTLV-I-negative T-cell lymphomas.

N-(4-hydroxyphenyl)retinamide induces growth arrest and apoptosis in HTLV-I-transformed cells.

N-(4-hydroxyphenyl)retinamide (HPR) is a synthetic retinoid that inhibits growth and induces apoptosis in many human cell lines. We explored the effects of HPR on human T-cell lymphotropic virus type I (HTLV-I)-positive and HTLV-I-negative malignant T-cell lines, most of which are resistant to all-trans retinoic acid. Clinically achievable concentrations of HPR caused a dramatic inhibition of cell proliferation, G(0)/G(1) arrest, and massive apoptosis in all tested malignant T cells, while no effect was observed on resting or activated normal lymphocytes. Interestingly, HTLV-I-negative cell lines were significantly more sensitive to HPR compared to HTLV-I-positive and Tax-transfected cells. In HTLV-I-negative cells only, HPR-induced apoptosis was associated with ceramide accumulation, sharp decrease in mitochondrial membrane potential, and activation of caspases 8, 9 and 3, and could be partially reverted by the caspase inhibitor z-VAD suggesting that Tax protects infected cells from ceramide accumulation and caspase-mediated apoptosis. In HTLV-I-positive cells, HPR treatment rapidly induced proteasomal-mediated degradation of p21, downregulated cyclin D(1), and upregulated bax protein levels. These findings support a potential therapeutic role for HPR in both HTLV-I-associated adult T-cell leukemia/lymphoma (ATL) and HTLV-I-negative peripheral T-cell lymphomas.

Homologous telomere association of 19q in a female with premature ovarian failure.

Premature ovarian failure (POF) may be due to a variety of genetic mechanisms. We report here, for the first time, telomere association of the long arms of chromosome 19, identified at low frequency (1%) in the peripheral blood cultures of a 30-year-old female with POF. Repeat cultures identified, in addition, the presence of 16q and 22q associations at a lower frequency (0.5%). These consistent observations are suggestive of a non-random event. Their association with POF may just be coincidental or may hypothetically explain it by an abnormal mechanism of chromosome separation, a constitutional telomere anomaly or an unidentified chromosome instability disorder.

Overexpression of retinoic acid receptors alpha and gamma into neoplastic epidermal cells causes retinoic acid-induced growth arrest and apoptosis.

Retinoids are essential for normal epidermal differentiation and are used for the prevention and treatment of numerous skin disorders and cancers in humans. In previous studies, we have shown that retinoic acid receptors (RARs) -alpha and -gamma are down-regulated during skin tumor progression. The transduction of v-ras(Ha) into primary mouse keratinocytes is sufficient to reduce both RARalpha and RARgamma protein levels as well as inhibit their transactivation functions. Our primary objective is to investigate the roles that RARalpha and RARgamma play in keratinocyte tumor cell proliferation. Through retroviral gene transduction, we overexpressed RARalpha or RARgamma into neoplastic mouse epidermal cells with down-regulated endogenous RAR proteins. Following all-trans retinoic acid (RA) treatment, RARalpha- and RARgamma-transduced cell lines exhibit a progressive, dose-dependent growth inhibition relative to the control LXSN cell lines. Further characterization of RAR-transduced cells following RA treatment reveals that both RARalpha and RARgamma cause a decrease in S-phase population, while only RARalpha causes a simultaneous G(0)/G(1) block as evidenced by reduced [(3)H]-thymidine incorporation and flow cytometric analysis of DNA content. Following RA treatment, both receptors cause an early, transient increase in the cyclin-dependent kinase inhibitor (CDKI) p21 proteins, while only RARalpha causes a simultaneous sharp, brief increase in the CDKI p16 protein. A later decrease in cyclin D(1) protein is also evident in RARalpha- and RARgamma-transduced cells. Chromatin condensation and PARP cleavage are observed in both RARalpha- and RARgamma-transduced cells indicating an RA-induced apoptosis that may be caspase dependent. Furthermore, both receptors cause a late upregulation and apparent cleavage of the squamous differentiation marker protein kinase C (PKC)-eta. These results suggest that RARalpha and RARgamma enhance growth suppression and apoptosis of neoplastic epidermal keratinocytes. This growth inhibitory effect of both retinoid receptors in neoplastic keratinocytes may be achieved through distinct as well as overlapping mechanisms of cell cycle control.

Retinoic acid dramatically enhances the arsenic trioxide-induced cell cycle arrest and apoptosis in retinoic acid receptor alpha-positive human T-cell lymphotropic virus type-I-transformed cells.

INTRODUCTION: Adult T-cell leukemia/lymphoma, caused by the human T-cell lymphotropic virus type I, is an aggressive neoplasm of mature activated T cells that is generally resistant to conventional therapy. While arsenic trioxide (As) inhibits the growth and induces apoptosis in HTLV-I-infected T cells, synergistically, when combined with interferon-alpha, variable effects on growth with all trans retinoic acid treatment have been reported in ATL-derived cell lines and fresh ATL cells. In this study, we investigate the effects of ATRA alone or in combination with As in HTLV-I-transformed cells. MATERIALS AND METHODS: Four HTLV-I-transformed cell lines (HuT-102, MT2, C8166 and C91PL) were treated with different doses of ATRA alone or in combination with As for one to three days. Cell growth was assessed by cell count with 3H-thymidine incorporation. Cell cycle distribution was assessed by propidium iodine-labeled DNA content by flow cytometry. Apoptosis was evaluated by Hoechst nuclear staining and annexin-V binding assays. Expression of retinoid receptors, the viral transactivator Tax, and the proteins bcl-2 and IkappaB-alpha proteins, was analysed by Western blot. RESULTS: Only C8166 cells were sensitive to the ATRA-induced growth inhibitory effect while HuT-102, MT2, and C91PL were resistant to ATRA treatment (up to 10(-5) M). The retinoid X receptor alpha and the retinoic acid receptor gamma (RARgamma) proteins were expressed in all four cell lines, while RARalpha protein was only detected in the HuT-102 and C8166 cells. The combination ATRA/As showed a highly synergistic effect on HuT-102 cells, and, to a lesser extent, on C8166 cells and resulted in a dramatic inhibition of cell proliferation and induction of massive apoptosis in HuT-102 cells, associated with caspase activation. While ATRA alone had no effect on Tax and IkappaB-alpha protein levels, ATRA increased the As-induced Tax degradation and the up-regulation of IkappaB-alpha protein. In contrast, the expression of bcl-2 protein was not significantly affected by any of the treatments. CONCLUSION: Our data provide a rationale for combined ATRA and As-therapies in ATL patients refractory to conventional therapy and expressing RARalpha in their leukemic cells.

Constitutional chromosome abnormalities among patients referred for blood karyotype analysis: a 5-year study at the AUBMC.

We report results on 2010 cases of blood referred for constitutional karyotype analysis. Referrals were grouped into 16 different categories, of which reproductive failure represented the highest percentage (33%), followed by structural congenital abnormalities (14.17%), developmental delay (11.34%), Down syndrome (9.65%), and abnormal sexual development (8.16%), while other categories represented smaller percentages. The total rate of abnormality was 16%, and the highest abnormality rates were among the clinically-recognizable chromosomal syndromes, while lower percentages were detected among less specific referrals. However, abnormality rates were generally different from the typical reported rates, probably due to the inclusion of cases not requiring chromosome analysis or the failure to recognize specific chromosomal syndromes. Other identified problems included lack of proper phenotypic description and difficulty in obtaining familial follow-up for proper diagnosis and genetic counseling.

Evidence against a direct cytotoxic effect of alpha interferon and zidovudine in HTLV-I associated adult T cell leukemia/lymphoma.

The combination of the anti-viral agents, zidovudine (AZT) and interferon-alpha (IFN), is a potent treatment of HTLV-I-associated adult T cell leukemia/lymphoma (ATL). In this study we investigate the possible mechanism of action of this combination by examining several cellular parameters including cell proliferation, cell cycle distribution and apoptosis. The ATL-derived T cell lines HuT-102 and MT-2 served as models. HTLV-I negative T cell lines (CEM and Jurkat) were used as controls. No significant modification of cell growth was observed except at suprapharmacological doses of AZT and IFN. Moreover, these effects were less pronounced in HTLV-I-infected cell lines compared to control cell lines. AZT and IFN treatment did not induce any significant modification of the expression of bcl-2 and p53. Interestingly no in vitro cytotoxic effect of AZT/IFN combination was observed on fresh leukemic cells derived from an acute ATL patient at diagnosis despite achievement of in vivo complete remission using the same therapy. These results suggest that the therapeutic effect of AZT and IFN is not through a direct cytotoxic effect of these drugs on the leukemic cells.

Karyotype of amniotic fluid cells at the AUB-MC results on 2000 cases.

We report results on 2000 cases of amniotic fluid referred for karyotype analysis. Referrals were advanced maternal age in 64% of cases and abnormal ultrasound in 12% of cases. The frequency of chromosome aneuploidy was 2.4% in the first category and that of chromosome abnormalities 8% in the second. The incidence of marker chromosomes was 0.25%, that of mosaicism 0.3%, and maternal cell contamination was observed in 0.6% of cases. The overall culture failure rate was 0.9%. Our results are mostly in accordance with figures from larger surveys, published in the literature and differences might be due to the smaller number of samples in this series and variation in referral and/or sampling protocols.

Characterization of the components of the putative mammalian sister chromatid cohesion complex.

Establishing and maintaining proper sister chromatid cohesion throughout the cell cycle are essential for maintaining genome integrity. To understand how sister chromatid cohesion occurs in mammals, we have cloned and characterized mouse orthologs of proteins known to be involved in sister chromatid cohesion in other organisms. The cDNAs for the mouse orthologs of SMC1S.c. and SMC3S.c. , mSMCB and mSMCD respectively, were cloned, and the corresponding transcripts and proteins were characterized. mSMCB and mSMCD are transcribed at similar levels in adult mouse tissues except in testis, which has an excess of mSMCD transcripts. The mSMCB and mSMCD proteins, as well as the PW29 protein, a mouse homolog of Mcd1pS.c./Rad21S.p., form a complex similar to cohesin in X. laevis. mSMCB, mSMCD and PW29 protein levels show no significant cell-cycle dependence. The bulk of the mSMCB, mSMCD and PW29 proteins undergo redistribution from the chromosome vicinity to the cytoplasm during prometaphase and back to the chromatin in telophase. This pattern of intracellular localization suggests a complex role for this group of SMC proteins in chromosome dynamics. The PW29 protein and PCNA, which have both been implicated in sister chromatid cohesion, do not colocalize, indicating that these proteins may not function in the same cohesion pathway. Overexpression of a PW29-GFP fusion protein in mouse fibroblasts leads to inhibition of proliferation, implicating this protein and its complex with SMC proteins in the control of mitotic cycle progression.

Mouse Sprr2 genes: a clustered family of genes showing differential expression in epithelial tissues.

Small proline-rich (SPR) proteins are structural components of the cornified cell envelope of stratified squamous epithelia. They are subdivided into three families, i.e., SPR1, SPR2, and SPR3, of which the SPR2 family is the most complex. To understand the significance of this complexity, we have isolated 11 mouse Sprr2 genes, constructed a provisional physical map of the Sprr2 locus on mouse Chromosome 3, and examined the expression patterns of the Sprr2 genes in mouse epithelial tissues. The 11 Sprr2 sequences are highly conserved with a central domain containing a variable number of repeats. In situ hybridization showed the Sprr2 expression to be confined to epithelia. RT-PCR using primers specific for each of the 11 Sprr2 members demonstrated varying degrees of expression among the individual Sprr2 members in different tissues. The correlation between the physical location of the genes in the Sprr2 locus and their expression patterns suggests multiple levels of controlled expression.

Topical retinoic acid reduces skin papilloma formation but resistant papillomas are at high risk for malignant conversion.

Retinoic acid (RA) was topically applied to the skin of Sencar mice during the promotion phase of specific tumor induction protocols that produce papillomas at low (12-O-tetradecanoylphorbol-13-acetate promoted, TPA) or high (mezerein-promoted) risk for premalignant progression and malignant conversion. RA consistently reduced the yield of papillomas and carcinomas in both protocols, but the frequency of malignant conversion in papillomas that emerged during RA treatment was not reduced. When TPA was reapplied after cessation of RA treatment, the number of papillomas increased 2-fold, suggesting that RA had not eliminated initiated cells. In vitro, RA prevented the emergence of transformed keratinocytes in an assay that mimics malignant conversion, suggesting that RA can suppress conversion if applied during the stage of premalignant progression. Examination of tumor markers at weeks 14 and 22 of the tumor-induction experiments in vivo indicated that papillomas evolving during RA treatment exhibited a phenotype of high progression risk, even in the TPA-promoted groups. In the majority of these tumors, the alpha6beta4 integrin and retinoid X receptor alpha transcripts were detected suprabasally, indicating an advanced state of premalignant progression. RA-treated tumors also expressed higher levels of transcripts for transforming growth factor (TGF)-beta1 and localized TGF-beta1 peptide in the basal portions of the tumor fronds. Because up-regulated expression of TGF-beta1 suppresses papilloma formation, these studies suggest a mechanism whereby RA can prevent papilloma eruption via a TGF-beta intermediate, but papillomas resistant to RA may have altered TGF-beta signaling and progress to carcinomas at an increased frequency.

Expression of a binding protein for FGF is associated with epithelial development and skin carcinogenesis.

Fibroblast growth factors (FGF)-1 and -2 are found in most embryonic and adult normal and tumor tissues, where they are immobilized in the extracellular matrix (EM). Mobilization of these FGFs is part of a tightly controlled process resulting in the activation of high-affinity receptors. Recently, we have shown that a novel human FGF-binding protein (FGF-BP) mediates the release of immobilized FGF-2 from the EM. Here we isolated genomic and cDNA clones of the mouse FGF-BP homologue and studied its expression during embryonic development and skin carcinogenesis. The murine gene contains two exons that generate a 1.2 kb mRNA and predicts an 18 kDa secreted protein that is 63% identical to its human homologue. FGF-BP mRNA expression during embryogenesis is restricted to skin, intestine and lung. In the developing skin, FGF-BP expression starts at embryonic day 9, reaches peak levels perinatally and is downregulated during postnatal development. Development regulation in the intestine is similar, but in lungs and ovaries high expression was also observed in the adult. FGF-BP mRNA expression in the adult skin is dramatically increased during early stages of carcinogen-induced transformation in vivo and by ras-activation in vitro. Finally, mouse FGF-BP binds to FGF-2 and can function as a modulator of FGF in FGF-responsive cells. Our results suggest a potential function of FGF-BP during development and tumorigenesis.

Loss of retinoic acid receptors in mouse skin and skin tumors is associated with activation of the ras(Ha) oncogene and high risk for premalignant progression.

Retinoic acid receptor transcripts (RARalpha and RARgamma) are decreased in benign mouse epidermal tumors relative to normal skin and are almost absent in carcinomas. In this report, the expression of RARalpha and RARgamma proteins was analyzed by immunoblotting in benign skin tumors induced by two different promotion protocols designed to yield tumors at low or high risk for malignant conversion. RARalpha was slightly reduced in papillomas promoted with 12-O-tetradecanoylphorbol-13-acetate (low risk) and markedly decreased or absent in papillomas promoted by mezerein (high risk). However, mezerein also caused substantial reduction of RARalpha in nontumorous skin. RARgamma was not detected in tumors from either protocol and was greatly reduced in skin treated by either promoter. Both RARalpha and RARgamma proteins were decreased in keratinocytes overexpressing an oncogenic v-ras(Ha) gene, and RARalpha was underexpressed in a benign keratinocyte cell line carrying a mutated c-ras(Ha) gene. Introduction of a recombinant RARalpha expression vector into benign keratinocyte tumor cells reduced the S-phase population and inhibited [3H]thymidine incorporation in response to retinoic acid. Furthermore, transactivation of B-RARE-tk-LUC by retinoic acid was markedly decreased in keratinocytes transduced with the v-ras(Ha) oncogene (v-ras(Ha)-keratinocytes). Blocking protein kinase C function in v-ras(Ha)-keratinocytes with bryostatin restored RARalpha protein to near normal levels, reflecting the involvement of protein kinase C in RARalpha regulation. Both RARalpha and RARgamma are down-regulated in cultured keratinocytes by 12-O-tetradecanoylphorbol-13-acetate, further implicating PKC in the regulation of retinoid receptors. Our data suggest that modulation of RARs could contribute to the neoplastic phenotype in mouse skin carcinogenesis and may be involved in the differential promoting activity of mezerein and 12-O-tetradecanoylphorbol-13-acetate, particularly for selecting tumors at high risk for malignant conversion.

Estrogen induces retinoid receptor expression in mouse cervical epithelia.

Steroid hormones and retinoids are powerful regulators of normal epithelial differentiation and function in the mouse female reproductive tract, where their actions are mediated by nuclear receptors. The expression pattern, heterodimeric interactions, and availability of ligand of these transcription factors are thought to contribute to the biological response. Estrogen (E2) induces proliferation and squamous differentiation of the cervical and vaginal epithelium during the mouse estrous cycle, while progesterone and retinoids maintain the simple columnar epithelium of the endocervix and uterine horns. We wanted to investigate whether retinoid receptors are responsive to estrogen status during cervical epithelial differentiation induced by a single dose of estrogen in ovariectomized adult mice. Northern blot analysis demonstrated a prolonged induction of RXR alpha and RAR gamma gene expression by E2 in the mouse cervix and vagina. When the induction of RXR alpha and RAR gamma was compared to genes known to be responsive to E2, including estrogen receptor (ER) and c-fos, RXR alpha was induced within 0.5 h of hormone treatment, while RAR gamma induction was evident by 4 h. The induction of these retinoid receptors suggests that they may be implicated in epithelial growth and differentiation in response to E2. Moreover, potential heterodimeric interactions among these receptors indicate that normal, cyclical epithelial differentiation results from the interplay of these molecules. Using in situ hybridization analysis, RXR alpha transcripts were localized preferentially in the basal cells, while ER mRNA was expressed throughout the epithelium of the ectocervix and vagina. Furthermore, ER transcripts were highly expressed in the stratified squamous foci induced by mild vitamin A depletion in the columnar epithelium of the endocervix and uterine horns. Therefore, the induction of RXR alpha and RAR gamma by E2 and their expression pattern in relation to ER suggest that they are needed to coordinate specific genetic programs that result in cervical epithelial growth and differentiation.

Retinoic acid down-regulation of fibronectin and retinoic acid receptor alpha proteins in NIH-3T3 cells. Blocks of this response by ras transformation.

All-trans-retinoic acid (RA) markedly reduced the level of intracellular fibronectin (FN) in a time- and concentration-dependent fashion in NIH-3T3 cells, but not in NIH-3T3 cells transformed by an activated Ha-ras oncogene. Pulse/chase experiments indicated that RA affects FN biosynthesis rather than its turnover rate. Steady state levels of FN transcripts did not change after treatment of the cells with RA for various times or concentrations, suggesting that RA acts at the translational level. Similar effects were observed in other fibroblasts. In NIH-3T3 cells, RA had distinct effects on different receptors; it down-modulated retinoic acid receptor (RAR) a protein and transcript levels, it up-regulated RAR beta transcripts, and it had no effect on RAR gamma. Transformation of NIH-3T3 cells with an activated Ha-ras oncogene down-modulated RAR expression and abolished responsiveness to RA. We identified the retinoid signal transduction pathways responsible for the effects of RA on FN and RAR alpha proteins by the use of the retinoid X receptor-selective compound, SR11237, by stable over-expression of a truncated form of the RAR alpha gene, RAR alpha 403 with strong RAR dominant negative activity, and by overexpression of RAR alpha. We conclude that: 1) RA-dependent FN down-modulation is mediated by RARs, 2) retinoid X receptors mediate the observed reduction of RAR alpha by RA, and 3) the block of RA responsiveness in Ha-ras cells cannot be overcome by overexpression of RAR alpha. These studies have defined fibronectin and RAR alpha as targets of RA in fibroblast cells and have shown that oncogenic transformation renders the cells resistant to RA action.

Sequence and expression patterns of mouse SPR1: Correlation of expression with epithelial function.

A final event in the terminal differentiation of stratified squamous epithelia is the formation of a cornified cell envelope, which is a complex of several proteins cross-linked together by transglutaminases. One set of proteins is the family of small proline rich (SPR) proteins. In human foreskin epidermal cell envelopes, SPRs serve as cross-bridging proteins among the more abundant loricrin. In order to study further their evolution and expression, we have isolated and sequenced cDNAs encoding two mouse SPR1 proteins, SPR1a and SPR1b Comparative sequence analysis showed the preservation of the overall structure of mammalian SPR1 proteins with highly conserved termini and a central peptide domain repeated 13 (SPE1a) or seven (SPR1b) times. Tissues obtained from mouse fetal, newborn, and adult skin were tested by Northern blot analyses, in situ hybridization and immunohistochemistry using an antibody raised to a synthetic peptide corresponding to the C terminus of the SPR1a protein. Skin expression was first detected in fetal periderm in anagen hair follicles of newborn and older mice, and in the thickened epidermis of the lip and footpad, but no signal was detected in interfollicular trunk epidermis. High levels of SPR1a expression were found in epithelia from the forestomach and penis, and in benign squamous papillomas. Other epithelia expressing SPR1a include the tongue, esophagus, and vagina. Whenever detected, SPR1a positive staining was present in the spinous and granular layers. In the forestomach and papillomas, the periphery of cells in the cornified layer was also stained. Our results suggest that SPR1a participates widely in the construction of cell envelopes in cornifying epithelia characterized by either increased thickness or a requirement for extreme flexibility. Based on its likely function as a cross-bridging protein in cell envelopes, we conclude that the mechanical attributes of cell envelopes may be determined in part by the SPR1 content, in accordance with the specific function of the epithelium.

Mouse skin tumor progression results in differential expression of retinoic acid and retinoid X receptors.

Retinoids are powerful regulators of epidermal cell growth and differentiation and are widely used in the prevention and treatment of skin disorders and cancers in humans. Since many of the effects of retinoids on cell growth and differentiation are mediated by nuclear retinoid receptors (RARs and RXRs), we were interested in determining RAR and RXR gene expression during mouse skin tumor progression. The two-stage system of mouse skin carcinogenesis was used to generate papillomas and carcinomas, and the different stages of malignant progression (papillomas, differentiated squamous cell carcinomas, undifferentiated squamous cell carcinomas, and spindle cell carcinomas) were characterized in each tumor by specific keratin expression prior to receptor characterization. Using in situ hybridization analysis, we show that the two major RAR isoforms (alpha 1 and gamma 1), which account for most of RARs in the skin, were expressed in both the basal and suprabasal layers in mouse epidermis. In contrast, RXR alpha transcripts were compartmentalized to the basal cell layers and concentrated in hair follicles. During skin tumor progression, RAR (alpha 1 and gamma 1) transcripts were down-modulated in malignant tumor cells, whereas RXR (alpha and beta) transcript expression was expanded in papillomas and carcinomas as the number of undifferentiated cells also increased. RXR gamma was not detected in the skin or at any stage during skin tumor progression. Spindle cell tumors lacked markers of the keratinocyte phenotype and lost RAR expression, yet retained expression of RXR alpha and beta. The increased abundance of transcripts for RXRs and decreased presence of RARs in skin tumor progression may favor other nuclear signal transduction pathways requiring RXR for heterodimer formation and contribute to phenotypic progression of cancer cells.

Autocrine transforming growth factor alpha is dispensible for v-rasHa-induced epidermal neoplasia: potential involvement of alternate epidermal growth factor receptor ligands.

Autocrine epidermal growth factor receptor activation by transforming growth factor alpha (TGF alpha) has been implicated in growth stimulation during epithelial neoplasia. Using keratinocytes isolated from mice with genetic defects in TGF alpha expression, we tested whether TGF alpha is required for transformation by the v-rasHa oncogene. Introduction of v-rasHa into primary epidermal cultures using a retroviral vector stimulated growth of both control (TGF alpha +/+, BALB/c) and TGF alpha-deficient (TGF alpha -/-, wa-1) keratinocytes. Moreover, v-rasHa elicited characteristic changes in marker expression (keratin 1 was suppressed; keratin 8 was induced), previously shown to be associated with epidermal growth factor (EGF) receptor activation, in both TGF alpha +/+ and TGF alpha -/- keratinocytes. v-rasHa markedly increased secreted (> 10-fold) and cell-associated (2-3-fold) TGF alpha levels in keratinocytes from TGF alpha +/+ and BALB/c mice, but not TGF alpha -/- or wa-1 mice. Based on Northern blot analysis, v-rasHa induced striking up-regulation of transcripts encoding the additional EGF family members amphiregulin, heparin-binding EGF-like growth factor, and betacellulin in cultured keratinocytes from all four mouse strains. Interestingly, in addition to the normal 4.5-kilobase TGF alpha transcript, wa-1 keratinocytes expressed two additional TGF alpha transcripts, 4.7 and 5.2 kilobases long. All three transcripts were up-regulated in response to v-rasHa, as well as exogenous TGF alpha or keratinocyte growth factor treatment, and were also detected in RNA isolated from wa-1 brain and skin. In vivo, v-rasHa keratinocytes from control as well as TGF alpha-deficient mice produced squamous tumors when grafted onto nude mice, and these lesions expressed high levels of amphiregulin, heparin-binding EGF-like growth factor, and betacellulin mRNA, regardless of their TGF alpha status. These findings indicate that TGF alpha is not essential for epidermal neoplasia induced by the v-rasHa oncogene and suggest that another EGF family member(s) may contribute to autocrine growth stimulation of ras-transformed keratinocytes.