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

The p16/MTS1/CDKN2 gene on human chromosome band 9p21 encodes two unrelated proteins: p16(INK4a), a inhibitor of the cyclin D-dependent kinases and CDK6, and the structurally unrelated p19(ARF) protein that arrests cell growth in G(1)/S and also in G(2)/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 p16 beta 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).