EXPRESSION OF THE PROENKEPHALIN GENE IN CULTURED ASTROGLIAL CELLS - ANALYSIS OF CELL-CYCLE DEPENDENCE

Glial progenitors strongly express the proenkephalin (PEnk) gene durin g their proliferation in the subventricular zone of the neocortex. Als o in primary culture, astroglial cells from rat neocortex produce PEnk mRNA. Since the basal expression sharply declines after the cultured cells reach confluence, it seems to be related to cell proliferation. In contrast, activation of protein kinases A and C strongly enhances t he levels of PEnk mRNA in confluent cultures. Therefore, it was invest igated in cultured neocortical astroglial cells, whether the basal and stimulated expression of the PEnk gene occurred during different phas es of the cell cycle. Activation of protein kinases A and C with 8Br.c AMP and tetradecanoylphorbolacetate, respectively, enhanced the PEnk g ene expression only during the G(1) phase. Unstimulated astroglial cel ls contained PEnk mRNA during the G(1) as well as the S phase of the c ell cycle. Since confluent astroglial cells are arrested in the G(1) p hase, they should have a basal expression of the gene which is compara ble to that in preconfluent cells. Thus, the reduced basal expression after confluence indicates that other mechanisms may play a role, such as humoral factors or contact inhibition.