Cyclin G2 expression during growth inhibition

We isolated and characterized cDXAs encoding murine cyclm (12 and examined the cell cycle dependent expression of cyclin (1'2 mRNA in marine H cell;-. We investigated the effect of various positive and negative stimuli on the expression of cyclin G2 transcripts in different maturation stage-specific innrine B cell lines. Upon treatment of B cells with the negative growth factor TGF-Jl or growth inhibiting corticostoroids. cyclin (12 m UN A levels are increased 10-11 fold. Although untreated immature B cells (WKHI-2;il and CHlil ) and B cell receptor (BCR} cross-linked or phorbol ester plus ionoinycin stimulated mature B cells (BAL-17 and CH 1'2} proliferate and express low levels of cyclin CI2 mRNA relative to cyclin 1)2. similarly stimulated immature B cells undergo growth arrest and apoptosis concurrent with an approximate ](} fold increase in cyclin G2 transcripts and decrease in cylin 1)2 niRNAs. In contract. BCR stimulated WKHI-231 phosphoinositide signaling mutants re sis-tani to BCR induced growth arrest did not display an increase in cyclin (12 or a decrease in cyclin 1)2 mRNAs. Costirnulation ol BCR challenged immature B cells with LPS or gp39 blocked cyclin G2 rnRXA upregulation and ihe concomitant growth arrest response. Rat cyclui (12 and cyclin I ha.s recently been cloned from a rat brain c.DNA library allowing an examination of its ex pression pattern in neuronal eell lines and tissues undergoing differentiation, growth arrest diid apoptosis.