The C-CRK gene, cellular homolog of the avian v-crk oncogene, encodes two alternatively spliced adaptor signaling
proteins, CRKI (28 kDa) and CRKII (40 kDa). Both CRKI and CRKII have been shown to activate
kinase signaling and anchorage-independent growth in vitro and CRKI transformed cells readily form
tumors in nude mice. Affymetrix
oligonucleotide arrays were used to analyse 86
lung adenocarcinomas and 10 uninvolved lung tissues. C-CRK
mRNA expression was increased in more advanced (stage III versus stage I), larger (T(2-4) versus T(1)), and poorly differentiated
tumors and in
tumors from patients demonstrating poor survival (P=0.00034). An overlapping series of 93
lung adenocarcinomas (64 stage I and 29 stage III) and 10 uninvolved lung specimens were measured for quantitative differences in CRKI and
CRKII protein levels using 2-D PAGE. CRK
protein spots were identified using mass spectrometry and 2-D Western blotting. A significant increase in levels of the CRKI
oncoprotein and the phosphorylated
isoform of CRKII was observed in
tumors (P<0.05). No difference in
protein level was evident between stages. Concordant with
mRNA expression, CRKI and CRKII were increased in poorly differentiated
tumors (P<0.05). CRK immunohistochemical analysis of
tumor tissue arrays using the same
tumor series also demonstrated increased abundance of nuclear and cytoplasmic CRK in more proliferative
tumors (P<0.05). This study provides the first quantitative analysis of discrete CRKI and
CRKII protein isoforms in human lung
tumors and provides evidence that the C-CRK proto-oncogene may foment a more aggressive phenotype in
lung cancers.