Induction of polyploidization in the human erythroleukemia cell line (HEL) by Protein kinase inhibitor (K252a) and the phorbol-Ester TPA

Abstract

Endomitosis (polyploidization) is a distinctive feature of megakaryocyte differentiation. We examined this mechanism in an erythromegakaryocytic cell line, HEL, using a protein kinase inhibitor K252a or a phorbol-ester TPA. HEL cells treated with K252a showed a marked increase in the proportion of CD41 positive cells and polyploid cells as well as in cellular size and nuclear size. TPA showed similar results but induced multi-nucleation instead of enlargement of nuclear size. K252a added at the GI/S boundary phase did not inhibit the first and second round DNA synthesis, but inhibited cell division. K252a did not inhibit the expression of genes involved in mitosis such as cyclin B, cdc25B and cdc2, in the first round S phase. However, the cyclin B associated Cdc2 kinase activity needed for mitosis during the G2/M phase was reduced by K252a. TPA delayed DNA synthesis and expression of these genes, and suppressed Cdc2 kinase activity in the second round G2/M phase. These results suggest that the polyploidization induced by K252a results from inhibiting mitosis possibly caused by suppression of Cdc2 kinase activity. TPA may induce the multi-nucleation through a different mechanism.

Key Words:

• Polyploidization
• megakaryocytic cell line
• K252a
• protein kinase inhibitor
• Cdc2 kinase