P16(INK4A) PROMOTES DIFFERENTIATION AND INHIBITS APOPTOSIS OF JKB ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS

Homozygous p16(INK4A) (p16) gene deletion is frequent in primary tumor cells from acute lymphoblastic leukemia (ALL), suggesting that loss o f p16 may be an important precursor to transformation in ALL. We have previously described JKB, a human ALL cell line, that contains homozyg ous deletion of the p16 gene. Because ectopic expression of p16 suppre sses cell growth, we created a temperature sensitive p16 mutant to dev elop a system for inducible p16 function in human ALL. JKB cells were transfected either with a p16 gene mutated at position 119 (E119G) to confer temperature sensitivity (JKB p16MT) or with control vector. The percentage of cells in G1 phase was similar in JKB control cells or i n JKB p16MT cells cultured at restrictive conditions (40 degrees C). H owever, with lowering of temperature from 40 degrees C to permissive c onditions (31 degrees C), the percentage of JKB p16MT cells in G1 phas e and binding of p16 to CDK4 and CDK6 increased, with associated decre ases in CDK4 and CDK6 kinase activities, and dephosphorylation of reti noblastoma protein (pRB). Culture of JKB p16MT cells at 31 degrees C f or greater than or equal to 13 days irreversibly inhibited growth. Mor eover, JKB p16MT cells cultured under these permissive conditions show ed a less transformed morphology and more differentiated phenotype tha n did these cells cultured under restrictive temperatures. Finally, de xamethasone (Dex) induced apoptosis of JKB p16MT cells cultured at 40 degrees C, but did not trigger death of these cells cultured at 31 deg rees C. These results suggest that deletion of p16 gene in JKB human A LL cells is associated with dysregulated growth of less differentiated tumor cells, which nonetheless remain susceptible to apoptosis trigge red by Dex. (C) 1997 by The American Society of Hematology.