Christopher J. Westlake, Ph.D.

The transmission of cellular signals via membrane transport is important for cell homeostasis, growth, motility, and communication. More than 60 Rabs and their associated effectors and modulators regulate membrane vesicle formation, transport, and fusion. Defects in Rab-dependent trafficking are associated with degenerative and neurological disorders and cancer. 


Rabs are activated to the GTP-bound state by guanine nucleotide exchange factors (GEF), which catalyze GDP release and reloading of GTP, and inactivated by GTPase-activating proteins (GAPs). In the active state, Rabs associate with effector proteins that are important for regulating membrane transport. Interestingly, Rabs have also been shown to bind GEFs and GAPs as effectors and this appears to be important for regulating downstream membrane trafficking steps. The overall focus of Dr. Westlake's research is on understanding the mechanisms that regulate Rab-dependent membrane transport important in signaling and disease.

One focus of the lab is to understand the molecular mechanism of the Rab11-Rab8 cascade important for primary cilium formation, termed ciliogenesis, and apical membrane formation in polarized cells. Rab8 was previously identified as a regulator of ciliogenesis following the discovery that Rabin8, the Rab8 GEF, associates with the BBSome, a core group of Bardet-Biedl syndrome (BBS) proteins. The primary cilium is present on most cells and defects associated with ciliary signaling, including the Sonic hedgehog pathway, have been linked to BBS and a growing list of genetic diseases and certain cancers.

Our prior work suggests that ciliogenesis initiation is preceded by the signaling-dependent binding of Rabin8 to Rab11. Rabin8 is transported via Rab11-recycling endosomes to the centrosome where Rab8 is activated to assemble the primary cilium membrane. We have developed advanced microscopy techniques to monitor in real-time the assembly of the primary cilium - a process completed in approximately 100 minutes.

Cell biology, proteomics, biochemistry and genetics approaches are being used to indentify and characterize associated factors in this pathway. As an example of this approach, mass spectrometry analysis of purified LAP (localization and affinity purification)-tagged Rabin8 was used to identify interactions with the TRAPPII complex, found to be required for Rabin8 centrosomal targeting and ciliogenesis. We are also investigating the roles of these and other membrane transport pathways in the sorting of receptors to the cilia and in the transmission of ciliary signals within the cell.