Expression of cell cycle regulating factor mRNA in small cell lung cancer xenografts

We have investigated the expression of cyclins, cyclin dependent kinases (CDK), and CDK inhibitors (CKI) at the mRNA level in a panel of small-cell lung cancer (SCLC) cell linesin vitro andin vivo as xenografts in nude mice. The results showed that the cell lines expressed varying amounts of most cyclin and CDK’s but only a few of the cell lines expressed cyclin D₁ and/or D₂ and some lacked expression of CDK6. Most cell lines expressed mRNA for the CKI’s but two cell lines lacked expression of p15^INK4B and p16^INK4A. The mRNA expression differed for a few of the cell lines regarding cyclin D₂ and CDK6 whenin vitro andin vivo data were compared. Two of the cell lines that express the retinoblastoma (Rb) protein had no sign of a deregulated Rb pathway but further studies at the protein level are necessary to demonstrate whether these two cell lines should have a normal Rb pathway or whether they will join the majority of cell lines with deregulated Rb pathway.