A POSITIVE EFFECT OF P21(CIP1 WAF1) IN THE COLONY FORMATION FROM MURINE MYELOID PROGENITOR CELLS AS ASSESSED BY RETROVIRAL-MEDIATED GENE-TRANSFER/

p21(cip1/waf1) is cyclin dependent kinase inhibitor, We have previousl y reported stimulation of p21(cip1/waf1) by steel factor and GM-CSF in a factor dependent cell Line and of p21(cip1/waf1) involvement in hem atopoiesis in vivo in p21(cip1/waf1) gene knockout (-/-) mice. To furt her assess, a role for increased p21(cip1/waf1) in hematopoietic proge nitor cells, we developed the retroviral vector L(p21(cip1))SN to tran scriptionally regulate p21(cip1/waf1) from the Mo-MLV LTR, L(p21(cip1) )SN and the control vector LXSN were used to transduce murine bone mar row progenitor cells from p21(cip1/waf1) (-/-) and littermate control (+/+) mice, as well as from other mouse strains, Hematopoietic colony formation by transduced cells was assessed in semi-solid culture mediu m with multiple growth factors, Myeloid colony formation by bone marro w cells from p21(cip1/waf1) (-/-) mice was significantly lower than th at by (+/+) mouse cells. Transduction of cells with LXSN had no effect on colony formation; however, (-/-) cells transduced with L(p21(cip1) )SN formed significantly greater numbers of colonies than either LXSN- transduced (-/-) or (+/+) cells. Moreover, L(p21(cip1))SN-transduced ( +/+) cells formed significantly more colonies than LXSN-transduced (+/ +) cells. Increased cloning efficiency of progenitors from normal stra ins of mice induced by L(p21(cip1))SN compared to LXSN-transduced cell s was seen whether unseparated or highly purified populations of Sca1( +)Lin(-) marrow cells were used. Gene transfer of L(p21(cip1))SN incre ased the size and number of cells per colony, as well as the number of colonies compared to LXSN gene transfer, No colonies grew from non-tr ansduced, LXSN-, or L(p21(cip1))SN-transduced cells when no growth fac tors were added to the cultures. These results document the positive e ffect of p21(cip1/waf1) in the proliferation and/or differentiation of the murine myeloid progenitor cells that lead to colony formation. (C ) 1998 Academic Press.