Dominant role of CDKN2B/p15INK4B of 9p21.3 tumor suppressor hub in inhibition of cell-cycle and glycolysis.

Human chromosome 9p21.3 is susceptible to inactivation in cell immortalization and diseases, such as cancer, coronary artery disease and type-2 diabetes. Although this locus encodes three cyclin-dependent kinase (CDK) inhibitors (p15INK4B, p14ARF and p16INK4A), our understanding of their functions and modes of action is limited to the latter two. Here, we show that in vitro p15INK4B is markedly stronger than p16INK4A in inhibiting pRb1 phosphorylation, E2F activity and cell-cycle progression. In mice, urothelial cells expressing oncogenic HRas and lacking p15INK4B, but not those expressing HRas and lacking p16INK4A, develop early-onset bladder tumors. The potency of CDKN2B/p15INK4B in tumor suppression relies on its strong binding via key N-terminal residues to and inhibition of CDK4/CDK6. p15INK4B also binds and inhibits enolase-1, a glycolytic enzyme upregulated in most cancer types. Our results highlight the dual inhibition of p15INK4B on cell proliferation, and unveil mechanisms whereby p15INK4B aberrations may underpin cancer and non-cancer conditions.

The long noncoding RNA Arrl1 inhibits neurite outgrowth by functioning as a competing endogenous RNA during neuronal regeneration in rats.

The intrinsic regeneration ability of neurons is a pivotal factor in the repair of peripheral nerve injury. Therefore, identifying the key modulators of nerve regeneration may help improve axon regeneration and functional recovery after injury. Unlike for classical transcription factors and regeneration-associated genes, the function of long noncoding RNAs (lncRNAs) in the regulation of neuronal regeneration remains mostly unknown. In this study, we used RNA-Seq-based transcriptome profiling to analyze the expression patterns of lncRNAs and mRNAs in rat dorsal root ganglion (DRG) following sciatic nerve injury. Analyses using the lncRNA-mRNA co-expression network, gene ontology enrichment, and Kyoto Encyclopedia of Genes and Genomes pathway databases indicated that the lncRNA Arrl1 decreases neurite outgrowth after neuronal injury. shRNA-mediated Arrl1 silencing increased axon regeneration both in vitro and in vivo and improved functional recovery of the sciatic nerve. Moreover, inhibiting an identified target gene of Arrl1, cyclin-dependent kinase inhibitor 2B (Cdkn2b), markedly promoted neurite outgrowth of DRG neurons. We also found that Arrl1 acts as a competing endogenous RNA that sponges a Cdkn2b repressor, microRNA-761 (miR-761), and thereby up-regulates Cdkn2b expression during neuron regeneration. We conclude that the lncRNA Arrl1 affects the intrinsic regeneration of DRG neurons by derepressing Cdkn2b expression. Our findings indicate a role for an lncRNA-microRNA-kinase pathway in the regulation of axon regeneration and functional recovery following peripheral nerve injury in rats.

Modified CDKN2B (p15) and CDKN2A (p16) DNA methylation profiles in urban pesticide applicators.

Gene-specific changes in DNA methylation by pesticides in occupationally exposed populations have not been studied extensively. Of particular concern are changes in the methylation profile of tumor-suppressor, such as CDKN2B and CDKN2A, genes involved in oncogenesis. The aim of this study was to evaluate the methylation profiles of CDKN2B and CDKN2A genes in urban pesticide applicators and their relationship with occupational exposure to pesticides. A cross-sectional study was conducted in 186 urban pesticide applicators (categorized as high or moderate exposures) and 102 participants without documented occupational exposures to pesticides. Acute and chronic pesticide exposures were evaluated by direct measurement of urinary dialkylphosphates, organophosphate metabolites, and a structured questionnaire, respectively. Anthropometric characteristics, diet, clinical histories, and other variables were estimated through a validated self-reported survey. DNA methylation was determined by pyrosequencing of bisulfite-treated DNA. Decreased DNA methylation of the CDKN2B gene was observed in pesticide-exposed groups compared to the non-exposed group. In addition, increased methylation of the CDKN2A promoter was observed in the moderate-exposure group compared to the non-exposed group. Bivariate analysis showed an association between CDKN2B methylation and pesticide exposure, general characteristics, smoking status, and micronutrients, while changes in CDKN2A methylation were associated with pesticide exposure, sex, educational level, body mass index, smoking status, supplement intake, clinical parameters, and caffeine consumption. These data suggest that pesticide exposure modifies the methylation pattern of CDKN2B and CDKN2A genes and raise important questions about the role that these changes may play in the regulation of cell cycle activities, senescence, and aging.

Direct CDKN2 Modulation of CDK4 Alters Target Engagement of CDK4 Inhibitor Drugs.

The interaction of a drug with its target is critical to achieve drug efficacy. In cases where cellular environment influences target engagement, differences between individuals and cell types present a challenge for a priori prediction of drug efficacy. As such, characterization of environments conducive to achieving the desired pharmacologic outcome is warranted. We recently reported that the clinical CDK4/6 inhibitor palbociclib displays cell type-specific target engagement: Palbociclib engaged CDK4 in cells biologically sensitive to the drug, but not in biologically insensitive cells. Here, we report a molecular explanation for this phenomenon. Palbociclib target engagement is determined by the interaction of CDK4 with CDKN2A, a physiologically relevant protein inhibitor of CDK4. Because both the drug and CDKN2A prevent CDK4 kinase activity, discrimination between these modes of inhibition is not possible by traditional kinase assays. Here, we describe a chemo-proteomics approach that demonstrates high CDK4 target engagement by palbociclib in cells without functional CDKN2A and attenuated target engagement when CDKN2A (or related CDKN2/INK4 family proteins) is abundant. Analysis of biological sensitivity in engineered isogenic cells with low or absent CDKN2A and of a panel of previously characterized cell lines indicates that high levels of CDKN2A predict insensitivity to palbociclib, whereas low levels do not correlate with sensitivity. Therefore, high CDKN2A may provide a useful biomarker to exclude patients from CDK4/6 inhibitor therapy. This work exemplifies modulation of kinase target engagement by endogenous proteinaceous regulators and highlights the importance of cellular context in predicting inhibitor efficacy.

SARAH Domain-Mediated MST2-RASSF Dimeric Interactions.

RASSF enzymes act as key apoptosis activators and tumor suppressors, being downregulated in many human cancers, although their exact regulatory roles remain unknown. A key downstream event in the RASSF pathway is the regulation of MST kinases, which are main effectors of RASSF-induced apoptosis. The regulation of MST1/2 includes both homo- and heterodimerization, mediated by helical SARAH domains, though the underlying molecular interaction mechanism is unclear. Here, we study the interactions between RASSF1A, RASSF5, and MST2 SARAH domains by using both atomistic molecular simulation techniques and experiments. We construct and study models of MST2 homodimers and MST2-RASSF SARAH heterodimers, and we identify the factors that control their high molecular stability. In addition, we also analyze both computationally and experimentally the interactions of MST2 SARAH domains with a series of synthetic peptides particularly designed to bind to it, and hope that our approach can be used to address some of the challenging problems in designing new anti-cancer drugs.

Polymorphisms in promoter sequences of the p15 ( INK4B ) and PTEN genes of normal Japanese individuals.

Gene promoter regions of p15(INK4B), a cyclin-dependent kinase inhibitor, and phosphatase and tensin homolog (PTEN), a dual-function protein and lipid phosphatase, interact with regulatory factors for gene transcription and methylation. Normal individuals exhibit sequence polymorphisms in these regulatory genes. We isolated genomic DNA from whole blood of healthy Japanese individuals and sequenced promoter regions of the p15 ( INK4B ) and PTEN genes. We also examined the influence of polymorphisms on promoter activity in several cell lines. We identified polymorphisms at positions -699, -394, and -242 and an insertion at position -320 in the p15 ( INK4B ) gene and a polymorphism at position -1142 in the PTEN gene. Reporter gene analysis revealed that these polymorphisms influenced transcriptional regulation in their cell lines. Our results indicate for the first time that promoter sequences of the p15 ( INK4B ) and PTEN genes differ among normal Japanese individuals and that promoter polymorphisms can influence gene transcription.

Disruption of chromosome 11 in canine fibrosarcomas highlights an unusual variability of CDKN2B in dogs.

BACKGROUND: In dogs in the western world neoplasia constitutes the most frequently diagnosed cause of death. Although there appear to be similarities between canine and human cancers, rather little is known about the cytogenetic and molecular alterations in canine tumours. Different dog breeds are susceptible to different types of cancer, but the genetic basis of the great majority of these predispositions has yet to be discovered. In some retriever breeds there is a high incidence of soft tissue sarcomas and we have previously reported alterations of chromosomes 11 and 30 in two poorly differentiated fibrosarcomas. Here we extend our observations and present a case report on detail rearrangements on chromosome 11 as well as genetic variations in a tumour suppressor gene in normal dogs. RESULTS: BAC hybridisations on metaphases of two fibrosarcomas showed complex rearrangements on chromosome 11, and loss of parts of this chromosome. Microsatellite markers on a paired tumour and blood DNA pointed to loss of heterozygosity on chromosome 11 in the CDKN2B-CDKN2A tumour suppressor gene cluster region. PCR and sequencing revealed the homozygous loss of coding sequences for these genes, except for exon 1beta of CDKN2A, which codes for the N-terminus of p14ARF. For CDKN2B exon 1, two alleles were observed in DNA from blood; one of them identical to the sequence in the dog reference genome and containing 4 copies of a 12 bp repeat found only in the canine gene amongst all species so far sequenced; the other allele was shorter due to a missing copy of the repeat. Sequencing of this exon in 141 dogs from 18 different breeds revealed a polymorphic region involving a GGC triplet repeat and a GGGGACGGCGGC repeat. Seven alleles were recorded and sixteen of the eighteen breeds showed heterozygosity. CONCLUSION: Complex chromosome rearrangements were observed on chromosome 11 in two Labrador retriever fibrosarcomas. The chromosome alterations were reflected in the loss of sequences corresponding to two tumour suppressor genes involved in cell-cycle progression. Sequencing of CDKN2B across many different breeds revealed a widespread polymorphism within the first exon of the gene, immediately before the ankyrin coding sequences.