Despite an intense focus on novel therapeutic strategies, pancreatic
adenocarcinoma remains one of the deadliest human
malignancies. The frequent and rapid mortality associated with
pancreatic cancer may be attributed to several factors, including late diagnosis, rapid
tumor invasion into surrounding tissues, and formation of distant
metastases. Both local invasion and
metastasis require disruption of
tumor cell contacts with the extracellular matrix. Detachment of normal cells from the extracellular matrix leads to a form of programmed cell death termed anoikis.
Pancreatic cancer cells avert anoikis by activation of signaling pathways that allow for adhesion-independent survival. In the present studies, cellular signaling pathways activated in detached
pancreatic cancer cells were examined. We demonstrate a rapid and robust activation of
Src kinase in detached
pancreatic cancer cells, relative to adherent. Src autophosphorylation rapidly returned to baseline levels upon reattachment to tissue culture
plastic, in the presence or absence of specific
extracellular matrix proteins. Treatment of
pancreatic cancer cells with
tyrosine phosphatase inhibitors increased steady-state Src autophosphorylation in adherent cells and abrogated the detachment-induced increase in Src autophosphorylation. Src was found to co-immunoprecipitate with the Src homology 2 (
SH2) domain containing protein tyrosine phosphatase (SHP-2) in
pancreatic cancer cells, suggesting that SHP-2 may participate in regulation of Src autophosphorylation in adherent cells.
Src family kinase (SFK) dependent increases in Akt and
Jun N-terminal kinase (JNK) phosphorylation were observed in detached cells, indicating the potential for Src-dependent activation of survival and stress pathways in
pancreatic cancer cells that have detached from the extracellular matrix.