The human protein p19(ARF) is not detected in hemopoietic human cell lines that abundantly express the alternative β transcript of the p16(INK4a)/MTS1 gene

The p16/MTS1/CDKN2 gene on human chromosome band 9p21 encodes two unrelated proteins: p16(INK4a), a specific inhibitor of the cyclin D-dependent kinases CKD4 and CDK6, and the structurally unrelated p19(ARF) protein that arrests cell growth in G₁/S and also in G₂/M. By use of polyclonal antibodies, the human p19(ARF) (hp19(ARF)) protein has been identified in the nucleus of various cells including normal cultured fibroblasts. The level of this protein did not fluctuate throughout the cell cycle and was more elevated in fibroblasts with limited or arrested growth, suggesting that p19(ARF) accumulated in presenescent or senescent cells, Interestingly, hp19(ARF) was not detected in several hemopoietic tumor cell lines (mainly of B-type lymphoid origin) that expressed abundant amounts of the p16β transcript. This finding indicates that in certain tumors, the expression of hp19(ARF) RNA and protein may be uncoupled. Furthermore, it suggests that disruption of a translational mechanism may be involved in the inactivation of hp19(ARF).