Dysregulation of the
plasminogen activation cascade is a prototypic feature in many malignant epithelial
cancers. Principally, this is thought to occur through activation of overexpressed
urokinase plasminogen activator (uPA) concomitant with binding to its high specificity
cell surface receptor urokinase plasminogen activator receptor (uPAR). Up-regulation of uPA and uPAR in
cancer appears to potentiate the malignant phenotype, either (i) directly by triggering
plasmin-mediated degradation or activation of uPA's or
plasmin's proteolytic targets (e.g., extracellular matrix
zymogen proteases or nascent
growth factors) or indirectly by simultaneously altering a range of downstream functions including signal transduction pathways ( Romer, J. ; Nielsen, B. S. ; Ploug, M. The
urokinase receptor as a potential target in
cancer therapy Curr. Pharm. Des. 2004, 10 ( 19), 235976 ). Because many malignant epithelial
cancers express high levels of uPAR, uPA or other components of the
plasminogen activation cascade and because these are often associated with poor prognosis, characterizing how uPAR changes the downstream cellular "
proteome" is fundamental to understanding any role in
cancer. This study describes a carefully designed proteomic study of the effects of antisense uPAR suppression in a previously studied
colon cancer cell line (HCT116). The study utilized replicate 2DE
gels and two independent gel image analysis software packages to confidently identify 64
proteins whose expression levels changed (by > or =2 fold) coincident with a moderate ( approximately 40%) suppression of cell-surface uPAR. Not surprisingly, many of the altered
proteins have previously been implicated in the regulation of
tumor progression (e.g.,
p53 tumor suppressor protein and c-myc oncogene
protein among many others). In addition, through a combination of proteomics and immunological methods, this study demonstrates that
stathmin 1alpha, a cytoskeletal
protein implicated in
tumor progression, undergoes a basic isoelectric point shift (p I) following uPAR suppression, suggesting that post-translational modification of
stathmin occur secondary to uPAR suppression. Overall, these results shed new light on the molecular mechanisms involved in uPAR signaling and how it may promulgate the malignant phenotype.