Expression of the focal adhesion protein paxillin in lung cancer and its relation to cell motility

Lung cancer can lead to abnormalities of the actin cytoskeleton structure w hich may be important in transformation. In this study, we have investigate d the expression of the cytoskeletal associated protein paxillin in lung ca ncer, Paxillin is a 68 kDa focal adhesion protein, with four tandem LIM dom ains at the C-terminus, involved in growth factor receptor, integrin and on cogenic signaling such as v-src, BCR/ABL, and E6 of the papilloma virus. In non-small cell lung cancer (NSCLC) cell lines, paxillin localized to the f ocal adhesions. The possible role of paxillin in lung cancer cells was asse ssed by overexpressing green fluorescence protein (GFP)-paxillin construct in two separate NSCLC cell lines (Calu-1 and H661), Over the course of 48 h , GFP-paxillin consistently caused the cells to become round and to decreas e cell motility as compared to normal controls, GFP-N-terminus paxillin, or GFP-LIM transfected cells. Because some lung cancers may be quite aggressi ve and metastasize quickly, which may be related to the cytoskeleton, we de termined the expression of paxillin in NSCLC and small cell lung cancer (SC LC) cell lines and patient tumor tissues. Expression of paxillin in NSCLC a nd SCLC cell lines were determined by Northern blot and Western blot analys is. The expression of paxillin was consistently low in SCLC cell lines, whe reas there was paxillin expression in NSCLC cell lines. There was a variabi lity of expression of paxillin in NSCLC tumor tissue as compared to normal lung tissue. In contrast, by immunohistochemistry, we show that there was n o detectable expression of paxillin in 5/5 SCLC patients. This data suggest s that absence or low level of paxillin protein expression may cause certai n lung cancers, such as SCLC, to be more motile and possibly more aggressiv e.