EXPRESSION OF THE P16 AND P15 CYCLIN-DEPENDENT KINASE INHIBITORS IN LYMPHOCYTE-ACTIVATION AND NEURONAL DIFFERENTIATION

The cyclin-dependent kinase inhibitors p16(INK4)/MTS1 and p15(INK4B)/M TS2 have been mapped to a region in chromosome 9 (p21) that is deleted frequently in acute lymphoblastic leukemias and malignant gliomas. To gain insight into the functions of these inhibitors in lymphocytes an d neuronal cells, we studied the expression of p15 and p16 during lymp hocyte mitogenesis and neuronal differentiation. Expression of p15 was extinguished during lymphocyte activation, concomitant with an increa se in retinoblastoma kinase activity. The differentiation of the embry onic teratocarcinoma cell line NT2 into postmitotic neurons (hNT) was associated with enhanced expression of p15 and p16 proteins. These fin dings suggest that p15 and p16 play a role in maintaining cell quiesce nce in lymphocytes and neuronal cells, respectively. Deletions of thes e genes may thus promote unrestrained growth.