Fig. 1.
Heterogeneity of steady-state SFK activity in a panel of 64 human CRC cell lines. (A) (Upper) Schematic representation of the human c-Src domain structure. Phosphorylation of Tyr-419 in the activation loop of the catalytic domain (corresponds to Tyr-416 in chicken c-Src) is crucial for tyrosine kinase activity. (Lower) Sequence alignment of all human SFK regions corresponding to the Tyr-419 epitope in human c-Src. Names of SFKs with detectable mRNA expression in CRC lines are in bold. Divergent amino acids in this conserved epitope are boxed. Note the high degree of sequence identity in this key regulatory epitope for all SFKs expressed in the CRC lines. (B) Western blots of total cell protein extracts from 64 human CRC lines grown as described in Methods were separated by SDS/PAGE and immunoblotted with the anti-phosphoTyr419Src antibody that recognizes the SFK members expressed in the CRC lines. Membranes were exposed to x-ray film for 1–2 min. Standardization of signal intensities between the four panels was done by using a single batch of lysate from K562 CML cells, which are known to contain activated SFKs. There is a striking degree of diversity in signal intensity and detectable band sizes. For longer exposures of the same blots, see SI Fig. 6E.