Activation of extracellular signal-regulated kinases (ERKs) defines the first phase of 1,25-dihydroxyvitamin D-3-induced differentiation of HL60 cells

Activation of ERK1 and ERK2 protein kinases has been implicated in diverse cellular processes, including the control of cell proliferation and cell di fferentiation (Marshal[ [1995] Cell 80:179). In human myeloblastoid leukemi a HL60 cells rapid (ca. 15 min) but transient activation of ERK1/2 has been reported following induction of macrophageimonocyle differentiation by pho rbol esters, or by very high (10(-6) M) concentrations of 1,25-dihydroxyvit amin D-3 (1,25D(3)), while retinoic acid-induced granulocytic differentiati on was accompanied by sustained activation of ERK1/2. We report here that m onocytic differentiation of HL60 cells induced by moderate (10(-9) to 10(-7 ) M) concentrations of 1,25D(3) could be divided into at least two stages. in the first phase, which lasts 24-48 h, the cells continued in the normal cell cycle while expressing markers of monocytic phenotype, such as CD14. I n the next phase the onset of G1 cell cycle block became apparent and expre ssion of CD11b was prominent, indicating a more mature myeloid phenotype. T he first phase was characterized by high levels of ERKs activated by phosph orylation, and these decreased as the cells entered the second phase, while the levers of p27/Kip1 increased at that time. Serum-starved or PD98059-tr eated HL60 cells had reduced growth rate and slower differentiation, but th e G1 block also coincided with decreased levels of activated ERK1/2. The da ta suggest that the MEK/ERK pathway maintains cell proliferation during 1,2 5D(3)-induced monocytic differentiation of HL60 cells, but that ERK1/2 acti vity becomes suppressed during the rater stages of differentiation, and the consequent G1 block leads to "terminal" differentiation. J. Cell. Biochem. 80:471-482, 2001. (C) 2001 Wiley-Liss, Inc.