CDKN2B (cyclin dependent kinase inhibitor 2B; HGNC:1788, NCBI Gene ID 1030) is a human locus mapped to chromosome band 9p21.3 that encodes four-ankyrin-repeat Cyclin-Dependent Kinase 4/6 inhibitor p15INK4b (138 aa; 15 kDa). CDKN2B acts in TGFB1-SMAD2/3/4 cytostatic G1 cell-cycle arrest & 9p21.3 vascular smooth muscle senescence locus, together with CDKN2A (Adjacent p16INK4a / p14ARF Gene at 9p21.3), p16INK4a Paralog Protein, and TGFB1 (Transforming Growth Factor Beta 1 Inducer). Encodes the p15INK4b cyclin-dependent kinase 4/6 inhibitor induced by TGF-beta signaling at the chromosome 9p21.3 tumor suppressor and coronary disease locus.
Co-deleted with CDKN2A in glioblastoma, T-ALL & pancreatic cancer; 9p21.3 CAD risk locus regulates vascular CDKN2B expression
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 2-exon gene located on chromosome 9p21.3 just 30 kb centromeric to CDKN2A within the INK4-ARF tumor suppressor cluster and overlapped in antisense orientation by the long non-coding RNA CDKN2B-AS1 (ANRIL), with a proximal promoter containing SMAD2/3/4 and FOXO binding sites (and an absence of MYC-MIZ1 repression when TGF-beta is active).
Cellular & Tissue Expression Profile: Induced up to 30-fold by transforming growth factor-beta (TGFB1) in epithelial cells, keratinocytes, hematopoietic progenitors, and vascular smooth muscle cells.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Shares ~80% sequence identity in its four ankyrin repeat domains with p16INK4a (CDKN2A): upon TGF-beta stimulation, newly synthesized p15INK4b binds CDK4 and CDK6, displacing p27Kip1 (which then redistributes onto Cyclin E-CDK2) so that both CDK4/6 and CDK2 are simultaneously inhibited, enforcing rapid hypophosphorylation of RB1 and G1 arrest.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Frequently co-deleted with adjacent CDKN2A in T-cell acute lymphoblastic leukemia, glioblastoma, and melanoma, or epigenetically silenced by CpG island hypermethylation in myelodysplastic syndromes and acute myeloid leukemia; furthermore, human coronary artery disease risk alleles at the 9p21.3 GWAS hotspot reduce vascular smooth muscle CDKN2B expression, promoting excessive smooth muscle proliferation and efferocytosis defects in atherosclerotic plaques.
Therapeutic & Clinical Pharmacology: Hypomethylating agents (azacitidine, decitabine) used in myelodysplastic syndromes and AML act in part by demethylating the CDKN2B promoter to restore p15INK4b-mediated cell-cycle restraint.