Adhesion Molecule Phosphorylation in Cancer Chemotherapy - Adhesion Molecules - page 345

Metastasis describes the process of cancer dissemination away from the primary
tumour and establishment of secondary tumours at distal sites. Integrin-based
interaction with the ECM is required for mesenchymal-type cell motility that is
observed in many metastasizing cancer cells. Very recently, it has become apparent
that migrating cancer cells can switch between integrin-dependent mesenchymal
motility and non-integrin-dependent motility (Friedl 2004); successful approaches
to block cancer metastasis may thus necessitate blocking of both migration modes.
Few therapies currently directly target metastasis, yet given the high burden of
mortality resulting from progression to metastatic disease there is considerable
scope for therapeutic improvements in this area.
ADHESION-ACTIVATED PHOSPHORYLATION
SIGNALLING CASCADES
Src Kinases
Enhanced Src kinase activity and elevated expression levels have been reported in a
wide variety of tumour types (Brunton et al. 2008). h is enzyme has potent kinase
activity and of all the molecules in the integrin adhesome displays the greatest
connectivity with other molecules in the network (Zaidel-Bar et al. 2007).
Phosphorylation of residue Y 530 in human c-Src carboxyl-terminal creates a
binding site for the amino-terminal Src SH2 domain, thereby forming an intra-
molecular interaction holding the molecule in a closed and inhibited conformation
(Fig. 3) . Src pY 530 de-phosphorylation releases this repression permitting auto-
phosphorylation of Y 418 in the kinase domain activation loop resulting in increased
kinase activity. Importantly, there are a number of commercially available robust
antibodies that are specii c for Src phosphorylation sites. h e most commonly
employed is anti-pY 418 as this site positively correlates with enzyme activity and is
generally accepted to provide a readout for increased Src activation. h e phospho-
specii c antibody ei ciently detects phosphorylated Src kinase on immunoblots
of protein extracts that have been separated by sodium-dodecyl-sulphate
polyacrylamide gel electrophoresis (SDS-PAGE) and this is a standard technique
for measuring Src activity in extracts from cultured cells (e.g., Cowell et al. 2006).
Increasingly, the phospho-specii c antibody is used for immunohistochemical
detection of phosphorylated and activated c-Src in patient tissue samples (e.g.,
Campbell et al. 2008).
FAK
Similar to Src, FAK expression levels and activity are elevated in a wide variety
of cancers, while elevated FAK expression correlates with increased metastatic
behaviour in colon, breast and ovarian tumours (Li et al. 2008). h e essential