Induction of differentiation accompanies inhibition of Cdk2 in a non-smallcell lung cancer cell line

Induction of differentiation in a variety of model systems is accompanied b y cell cycle exit and inhibition of Cdk2 kinase activity. We asked whether inhibition of Cdk2 activity is sufficient to allow differentiation to occur in a non-small cell lung cancer cell line. Treatment of NCI-H358 with flav opiridol, an inhibitor of multiple Cdk's, resulted in growth arrest and ind uction of mucinous differentiation. The onset of differentiation coincided temporally with loss of Cdk2 kinase activity. Western analysis revealed tha t flavopiridol treatment resulted in depletion of both cyclin E and D1, sug gesting that loss of the regulatory subunits is at least partially responsi ble for the loss of Cdk2 kinase activity. Similarly, roscovitine, an inhibi tor of Cdk's 1, 2, and 5, but not Cdk4, also induced differentiation in NCI -H358, although the resulting pattern of expression of cell cycle regulator y genes differed from the pattern obtained with flavopiridol. Furthermore, stable expression of an antisense Cdk2 construct in NCI-H358 also resulted in the appearance of a marker of mucinous differentiation. These results sh ow that the inhibition of activity of cyclin dependent kinases, particularl y Cdk2, by multiple different mechanisms is accompanied by differentiation. Thus, induction of differentiation is one potential mechanism of action fo r agents that down-regulate Cdk activity.