Interacts strongly with CDK4 and CDK6. Potent inhibitor. Potential effector of TGF-beta induced cell cycle arrest. Heterodimer of CDKN2B with CDK4 or CDK6. Isoform 2 does not interact with CDK4 nor CDK6. Also found in the nucleus. Isoform 2 is expressed in normal (keratinocytes, fibroblasts) and tumor cell lines. Belongs to the CDKN2 cyclin-dependent kinase inhibitor family.