LiHui Xu

Effect of focal adhesion kinase (FAK) downregulation with FAK antisense oligonucleotides and 5-fluorouracil on the viability of melanoma cell lines.

Inhibition of focal adhesion kinase (FAK), a non-receptor tyrosine kinase linked to tumour cell survival, causes cell rounding, loss of adhesion and apoptosis in human cancer cell lines. In this study, we tested antisense oligonucleotide inhibitors of FAK, in combination with 5-fluorouracil (5-FU), to increase its sensitivity in human melanoma cell lines. Antisense oligonucleotides directed to the 5′ mRNA sequence of FAK and missense control oligonucleotides were used. In BL melanoma cells, treatment with FAK antisense oligonucleotide was associated with a 2.5-fold increase in cell death compared with treatment with control oligonucleotide (33±2% vs. 13±3%, P<0.0001). 5-FU alone had no effect on BL cells (4.4% cell death, P=0.15). The addition of 5-FU after antisense oligonucleotide resulted in a significant synergistic increase in cell death equal to 69±2% compared with treatments with antisense oligonucleotide alone, 5-FU alone and control oligonucleotide (P<0.0001). Similar results were found in the C8161 melanoma cell line. In both cell lines, reduction in cell viability was accompanied by an increased loss of adhesion and increased apoptosis that was proportional to the decrease in viability. Treatment with antisense oligonucleotide plus 5-FU resulted in significantly decreased p125FAK expression in both C8161 and BL melanoma cell lines, demonstrated by Western blot analyses. These data show that the downregulation of FAK by antisense oligonucleotide combined with 5-FU chemotherapy results in a greater loss of adhesion and greater apoptosis in melanoma cells than treatment with either agent alone, suggesting that the combination may be a potential therapeutic agent for human melanoma in vivo.

Focal adhesion kinase N-terminus in breast carcinoma cells induces rounding, detachment and apoptosis.

Focal adhesion kinase (FAK) has a central role in adhesion-mediated cell signalling. The N-terminus of FAK is thought to function as a docking site for a number of proteins, including the Src-family tyrosine kinases. In the present study, we disrupted FAK signalling by expressing the N-terminal domain of FAK (FAK-NT) in human breast carcinoma cells, BT474 and MCF-7 lines, and non-malignant epithelial cells, MCF-10A line. Expression of FAK-NT led to rounding, detachment and apoptosis in human breast cancer cells. Apoptosis was accompanied by dephosphorylation of FAK Tyr(397), degradation of the endogenous FAK protein and activation of caspase-3. Over-expression of FAK rescued FAK-NT-mediated cellular rounding. Expression of FAK-NT in non-malignant breast epithelial cells did not lead to rounding, loss of FAK phosphorylation or apoptosis. Thus FAK-NT contributes to cellular adhesion and survival pathways in breast cancer cells which are not required for survival in non-malignant breast epithelial cells.

Breast cancer cell line proliferation blocked by the Src-related Rak tyrosine kinase

Rak is a 54 kDa protein tyrosine kinase originally isolated from breast cancer cells and expressed in epithelial cells. It resembles the protooncogene Src structurally but lacks an amino‐terminal myristylation site and localizes to the nuclear and perinuclear regions of the cell. We report here that expression of Rak in 2 different breast cancer cell lines inhibits growth and causes G1 arrest of the cell cycle. This growth inhibition is kinase‐dependent but does not require the Rak SH2 or SH3 domain. Rak also binds to the pRb tumor‐suppressor protein but inhibits growth even in cells that lack pRb. These results suggest that Rak regulates cell growth by phosphorylating perinuclear proteins and has a function that is distinct from the Src‐related kinase family.

The C-terminal domain of focal adhesion kinase reduces the tumor cell invasiveness in chondrosarcoma cell lines

Human chondrosarcoma is a malignancy that has no effective systemic therapy, making the interruption of the metastatic cascade critical to enhance patient survival. The processes of local invasion and metastases share similar mechanisms at a cellular level. Focal adhesion kinase (FAK) has been implicated in local invasion of malignant tumor cells. In the current manuscript we examine the effect of FAK inhibition on cell attachment to extracellular matrix (ECM) and in vitro invasion. Bovine articular chondrocytes and two human chondrosarcoma cell lines were utilized to examine FAK activity in tumor cell invasiveness. Endogenous FAK activity was inhibited by adenoviral transfection with the C‐terminal domain of FAK. This inhibition resulted from decreased FAK phosphorylation, while FAK expression remained unchanged. Inhibition of FAK phosphorylation and hence its activity lead to decreased cell adhesion to Type II collagen and decreased cell invasiveness. These effects were not due to changes in integrin expression, indicating that the inhibition was the result of disruption of outside: in signaling. There are three important aspects to these results. The first is that interruption of transmembrane signaling can affect cell attachment. The second is that in chondrosarcoma, cell differentiation correlates with FAK expression and metastatic potential. Thirdly, that cell invasiveness correlates with FAK activity and implies a mechanistic role for this molecular complex in local invasion and metastasis.