The role of Cdk5 in neuroendocrine thyroid cancer.

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer that originates from calcitonin-secreting parafollicular cells, or C cells. We found that Cdk5 and its cofactors p35 and p25 are highly expressed in human MTC and that Cdk5 activity promotes MTC proliferation. A conditional MTC mouse model was generated and corroborated the role of aberrant Cdk5 activation in MTC. C cell-specific overexpression of p25 caused rapid C cell hyperplasia leading to lethal MTC, which was arrested by repressing p25 overexpression. A comparative phosphoproteomic screen between proliferating and arrested MTC identified the retinoblastoma protein (Rb) as a crucial Cdk5 downstream target. Prevention of Rb phosphorylation at Ser807/Ser811 attenuated MTC proliferation. These findings implicate Cdk5 signaling via Rb as critical to MTC tumorigenesis and progression.

Secreted protein acidic and rich in cysteine as a regulator of murine ovarian cancer growth and chemosensitivity.

OBJECTIVE: Secreted protein acidic and rich in cysteine (SPARC) influences the growth of several solid tumors. Our objectives were to determine the effect of SPARC on the growth and response to cisplatin therapy of platinum-resistant ovarian cancer. STUDY DESIGN: SPARC expression was determined in 4 platinum-resistant ovarian cancer cell lines. The effect of increasing SPARC on cell proliferation was determined in vitro. The effect of host-derived SPARC on tumor growth and response to therapy was determined in vivo using the murine ovarian cancer cell line, OSEID8, which was injected into the peritoneum of wild-type (WT) and SPARC-null (SP-/-) mice. RESULTS: Forced expression of SPARC decreased growth of platinum-resistant ovarian cancer cell lines in vitro. In vivo, tumor growth was more aggressive in the absence of host-derived SPARC resulting in decreased survival compared with WT mice (P = .005). Cisplatin did not improve survival of WT mice. In contrast, cisplatin therapy resulted in a significant survival advantage (P = .0048) and decreased tumor volume (P = .02) in SP-/- animals. CONCLUSION: We conclude that SPARC is an important extracellular matrix protein that regulates the growth and chemosensitivity of ovarian cancer. In general, SPARC appears to control tumor cell growth but also impede the efficacy of cisplatin therapy. Therefore, selective inhibition of SPARC may provide an attractive strategy for increasing the efficacy of therapy in platinum-resistant ovarian tumors.

Semaphorin 3B inhibits the phosphatidylinositol 3-kinase/Akt pathway through neuropilin-1 in lung and breast cancer cells.

Semaphorin 3B (SEMA3B), located at 3p21.3, is a secreted member of the semaphorin family important in axonal guidance. SEMA3B undergoes allele and expression loss in lung and breast cancer and can function as a tumor suppressor. Previously, we found that SEMA3B induces apoptosis in tumor cells either by reexpression or when applied as a soluble ligand. SEMA3B-induced apoptosis was mediated, in part, by blocking vascular endothelial growth factor autocrine activity in tumor cells. In the current study, treatment of lung and breast cancer cells with picomolar concentrations of soluble SEMA3B inhibited their growth; induced apoptosis; and was associated with decreased Akt phosphorylation, increase in cytochrome c release and caspase-3 cleavage, as well as increased phosphorylation of several proapoptotic proteins, including glycogen synthase kinase-3beta, FKHR, and MDM-2. Lung and breast cancer lines resistant to SEMA3B did not show these signaling changes and a tumor-derived missense SEMA3B mutant was inactive in this regard, providing specificity. SEMA3B-mediated inhibition of proliferation and induction of apoptosis in cancer cells were blocked by expressing a constitutively active Akt mutant and are linked to tumor cell expression of neuropilin-1 (Np-1). SEMA3B-insensitive Np-1-negative tumor cells acquired sensitivity to SEMA3B after forced expression of Np-1, whereas SEMA3B-sensitive Np-1-positive tumor cells lost sensitivity to SEMA3B after knockdown of Np-1 by small interfering RNA. We conclude that SEMA3B is a potential tumor suppressor that induces apoptosis in SEMA3B-inactivated tumor cells through the Np-1 receptor by inactivating the Akt signaling pathway. CA118384

Anti-VEGF-A therapy reduces lymphatic vessel density and expression of VEGFR-3 in an orthotopic breast tumor model.

Because metastasis contributes significantly to cancer mortality, understanding its mechanisms is crucial to developing effective therapy. Metastasis is facilitated by lymphangiogenesis, the growth of new intratumoral or peritumoral lymphatic vessels from pre-existing vessels. Vascular endothelial growth factor A (VEGF-A) is a well-known angiogenic factor. Increasing evidence implicates VEGF-A in lymphangiogenesis, although the mechanism of its pro-lymphangiogenic effect is poorly understood. We examined the effect of the anti-VEGF-A neutralizing antibody 2C3 on tumor lymphangiogenesis and metastasis in an orthotopic breast carcinoma model using MDA-MB-231 cells and its luciferase-tagged derivative, 231-Luc(+) cells. Anti-VEGF-A antibody therapy reduced blood and lymphatic vessel densities by 70% and 80%, respectively, compared with the control antibody. Treatment with 2C3 antibody also decreased incidence of lymphatic and pulmonary metastases by 3.2- and 4.5-fold, respectively. Macrophage infiltration was reduced in 2C3-treated tumors by 32%, but VEGF-C expression was unchanged. In contrast, neoplastic cells and blood vessels in tumors from 2C3-treated mice expressed significantly less angiopoietin-2 (Ang-2) than tumors from control mice. The reduction in Ang-2 was associated with inhibition of VEGFR-3 expression in intratumoral lymphatic endothelial cells. Both VEGF-A and Ang-2 upregulated the expression of VEGFR-3 in cultured lymphatic endothelial cells. VEGF-A induced proliferation of lymphatic endothelial cells was reduced by 50% by soluble Tie-2, suggesting that Ang-2 is an intermediary of the pro-lymphangiogenic VEGF-A effect. These results suggest a novel mechanism by which anti-VEGF-A therapy may suppress tumor lymphangiogenesis and subsequent metastasis supporting the use of anti-VEGF-A therapy to control metastasis clinically.

Semaphorin 3B (SEMA3B) induces apoptosis in lung and breast cancer, whereas VEGF165 antagonizes this effect.

Semaphorin 3B (SEMA3B) is a secreted member of the semaphorin family, important in axonal guidance. We and others have shown that SEMA3B can act as a tumor suppressor by inducing apoptosis either by reexpression in tumor cells or applied as a soluble ligand. The common method of inactivation of SEMA3B is by allele loss and tumor-acquired promoter methylation. We studied the mechanism of SEMA3B-induced tumor cell apoptosis and found that vascular endothelial growth factor (VEGF)165 significantly decreased the proapoptotic and antimitotic effect of transfected or secreted SEMA3B on lung and breast cancer cells. VEGF165 binds to neuropilin, receptors for SEMA3B, and we found that SEMA3B competed for binding of 125I-VEGF165 to lung and breast cancer cells. We also found that small interfering RNA knockdown of tumor-produced VEGF-A or the use of an anti-VEGF neutralizing antibody (Ab) significantly inhibited tumor cell growth in vitro. By contrast, VEGF121, a VEGF variant that lacks binding to neuropilin (NP)-1 or NP-2 receptors, was not expressed in tumor cells and had no effect on SEMA3B growth-suppressing activities. In conclusion, we hypothesize that VEGF165, produced by tumor cells, acts as an autocrine survival factor and that SEMA3B mediates its tumor-suppressing effects, at least in part, by blocking this VEGF autocrine activity.

17 beta-estradiol- and 4-hydroxytamoxifen-induced transactivation in breast, endometrial and liver cancer cells is dependent on ER-subtype, cell and promoter context.

The pattern of transcriptional activation by 17beta-estradiol (E2) and 4-hydroxytamoxifen (4-OHT) was determined in ZR-75 and MDA-MB-231 breast, ECC1 and HEC1A endometrial and HepG2 liver cancer cell lines cotransfected with E2-responsive constructs and wild-type estrogen receptor alpha (ER alpha) or ER beta (ER beta) or variant forms of ER alpha expressing activation function 1, AF1 (ER alpha-AF1) or activation function 2, AF2 (ER alpha-AF2). The E2-responsive constructs contained promoter inserts from the human complement C3 (pC3), human cathepsin D (pCD) and rat creatine kinase B (pCKB) genes. Minimal ER beta-dependent transactivation (<2.5-fold induction) was observed for E2 only in ECC1 and MDA-MB-231 cells transfected with pCKB or pC3, whereas 4-OHT was inactive as an ER beta agonist for all promoters in the four cell lines. The ER alpha agonist and/or antagonist activities for E2 and 4-OHT were highly variable and the transactivation was dependent on ER subtype, ER alpha variant expressed, gene promoter, and cell context. For example, E2 did not activate pCD in HepG2 cells transfected with wild-type or variant ER alpha, whereas E2 activated reporter gene activity in the four endometrial and breast cancer cell lines transfected with ER alpha and pCD, pCKB or pC3. Hormone activation of these constructs by ER alpha-AF1 or ER alpha-AF2 was highly variable among the different cell lines and even in the same cell line transfected with the three E2-responsive constructs. Similar variability was observed for 4-OHT. For example, 4-OHT activates pC3 in HepG2 cells transfected with ER alpha or ER alpha-AF1, and pCKB in HEC1A cells. However, AF1-dependent activation by 4-OHT is not observed for pCKB in ECC1 cells or for pC3 and pCD in HEC1A or ECC1 endometrial cancer cells. The results of this study suggest that transcriptional activation by E2 and 4-OHT induces recruitment of different transcription factor complexes that are dependent on the cell type and also the gene promoter.