Expression of cyclin-dependent kinase inhibitor p15(INK4B) during normal and leukemic myeloid differentiation

Objective. Expression of the cyclin-dependent kinase inhibitor p15(INK4B) f requently is altered in myeloid malignancies. We previously demonstrated th at p15(INK4B) is expressed in normal myeloid cells. The aim of this study w as to investigate whether p15(INK4B) expression is restricted to the granul omonocytic lineage and to evaluate its modulation during normal and leukemi c myeloid differentiation. Materials and Methods. Normal CD34(+) cells were cultured in serum-free med ia to obtain granulomonocytic, erythroid, or megakaryocytic unilineage diff erentiation. NB4 promyelocytic cell line and fresh leukemic blasts from sev en patients with acute promyelocytic leukemia were cultured with all-trans retinoic acid. At different times of culture, cell samples were collected t o evaluate p15(INK4B) by semiquantitative reverse transcriptase polymerase chain reaction. Results. p15(INK4B) mRNA was found during granulomonocytic and megakaryocyt ic, but not erythroid, differentiation. In the granulomonocytic lineage, p1 5(INK4B) was detectable when the majority of cells were at the promyelocyti c stage and increased progressively in more mature elements. In the megakar yocytic Lineage, p15(INK4B) was expressed in the early phase of differentia tion, before megakaryoblasts had appeared, and was mantained throughout the time of culture, NB4 cell line and five of seven leukemic samples displaye d undetectable or very low level of p15(INK4B) that rapidly increased durin g retinoic acid-induced differentiation. Two leukemic samples (both collect ed from two patients developing all-trans retinoic acid syndrome) showed hi gh basal levels of p15(INK4D), which was not modified by retinoic acid trea tment. Conclusions. p15(INK4B) upregulation occurs specifically during normal gran ulomonocytic and megakaryocytic commitment. In acute promyelocytic leukemic blasts, p15(INK4B), which is detectable at a very low level, is promptly i ncreased by retinoic acid. In contrast, two acute promyelocytic leukemia sa mples obtained from patients who developed all-trans retinoic acid syndrome showed high basal levels of p15(INK4B) that did not increase further durin g all-trans retinoic acid-induced differentiation. (C) 2000 International S ociety for Experimental Hematology, Published by Elsevier Science Inc.