Modeling and targeting signal transduction pathways governing cell migration

Cell migration is a complex biophysical event that is dysregulated in a variety of human diseases including cancer. The ability of tumor cells to migrate enables cancer dissemination causing significant mortality thus making it an important therapeutic target. Motility is exhibited epigenetically by activation of numerous signaling pathways that transmit extracellular cues to the final effectors of cell movement. Such signaling switches are a part of larger and highly complex signaling (proteomic) networks that are under the control of numerous activators or inhibitors. Although majority of the proteins that are 'required' during cell motility have been identified, it is yet unclear wherein they fit within the signaling network to govern motility. Thus, a 'systems biology' approach is needed to understand the complex interplay of signaling cascades in mediating cell motility so that better therapeutic targets can be defined. We utilized a mathematical modeling approach, called decision tree analysis to map the interplay between five key signaling proteins known to regulate vital biophysical processes of fibroblast motility downstream of EGF receptor activation. Interestingly, our model identified myosin light chain (MLC) mediated cell contractility as a crucial node for maximal motility. Even more non-intuitively the decision tree model predicted that subtotal inhibition of MLC can actually increase motility. Confirmatory experiments with fibroblasts and cancer cells have shown that to be the case. Since the model proposed that total abrogation of contractility can limit cell migration, we asked if such an intervention can limit tumor invasion. Since PKCδ is implicated in EGF receptor mediated transcellular contractility, we abrogated PKCδ using pharmacological (Rottlerin) and molecular (RNAi) interventions. Such depletion of PKCδ reduced migration as well as invasiveness of prostate carcinoma cells predominantly by decreasing their contractility through myosin light chain (MLC). Additionally, activation of PKCδ correlated with human prostate cancer progression as assessed by immunohistochemistry of prostate tissue sections. In summation our studies illustrate the importance of quantitative (total versus subtotal) disruption of key signaling nodes in mediating a desired cell response. Novel computational modeling approaches are needed to identify newer molecular switches from existing proteomic networks that can be explored, using classical experimental methods, as therapeutic targets