DECREASED PHOSPHORYLATION OF A LOW-MOLECULAR-WEIGHT PROTEIN BY CGMP-DEPENDENT PROTEIN-KINASE IN VARIANT HL-60 CELLS RESISTANT TO NITRIC OXIDE-INDUCED AND CGMP-INDUCED DIFFERENTIATION

We previously described the isolation of a variant subline of HL-60 ce lls that does not differentiate in response to nitric oxide (NO)-gener ating agents or to cGMP analogs [7]. The variant cells have normal gua nylate cyclase activity and normal NO-induced increases in the intrace llular cGMP concentration. We now show that the variant cells have nor mal cGMP-dependent protein kinase (G-kinase) activity, both by an in v itro and in vivo assay, and using two-dimensional gel electrophoresis we have identified six G-kinase substrates in the parental cells. Of t hese six proteins, we found considerably less phosphorylation of one o f the proteins in the variant cells than in parental cells, both in vi tro and in intact cells, and by S-35-methionine/S-35-cysteine incorpor ation we found much less of this protein in the variant cells than in parental cells. The protein is a shared substrate of cAMP-dependent pr otein kinase (A-kinase); since cAMP analogs still induce differentiati on of the variant cells, it appears that the NO/cGMP/G-kinase and cAMP /A-kinase signal transduction pathways share some but not all of the s ame target proteins in inducing differentiation of HL-60 cells.