Receptor tyrosine kinases (RTKs) play a fundamental role in cell growth, metabolism and survival. Altered cell surface expression of RTKs has profound effects on organismal physiology and is associated with both metabolic disease and neoplasia. The insulin receptor (IR) is a prototypical RTK that regulates metabolism and lifespan and as such, insights from studies on IR homeostasis may be extended to other members of the RTK family. I have discovered that eliminating AKT, a critical kinase downstream of the IR, increased IR expression and decreased its degradation. Interestingly, expression of other RTKs such as EGFR and IGF-1R was also upregulated when PI3K/AKT/mTOR signaling was inhibited, suggesting common regulatory mechanisms to control RTK expression and degradation. In addition, inhibiting PI3K signaling attenuated degradation of the insulin receptor induced by metabolic inhibitors. These data suggest that negative feedback mechanisms exist for the highly conserved PI3K/AKT/mTOR pathway at both transcriptional and post-translational levels to regulate RTK stability, in coordination with nutrient status, in mammalian systems. To further investigate regulation of RTK expression at the earliest steps of its biogenesis, I have also examined how molecular chaperones that are partitioned in the ER luminal surface and cytosol collaborate to ensure protein maturation under the strict quality control system in the ER. I found that the ER chaperone calreticulin (CRT) and the cytosolic chaperone Hsp90 stabilized receptor expression through distinct pathways. In addition, live cell imaging using novel green fluorescent protein (GFP) chimeras of the IR revealed that movement of the receptor through the ER was accelerated by misfolding or by overexpression of either CRT or Hsp90. Our results indicate that both CRT and Hsp90 control IR expression at its earliest maturation stages and modulate its movement within the ER. Together, these studies elucidate the distinct molecular mechanisms involved in the dynamic regulation of IR homeostasis and suggest reciprocal interactions between insulin signaling, glucose metabolism and IR expression.

Last modified

• 08/27/2018

Creator

• Maria Rowena Bernadette Rojas Ramos

DOI

• https://doi.org/10.21985/N28424

Subject

• Interdepartmental Biological Sciences Program

Keyword

• Cell Biology

Date created

• 2007-12-07

Resource type

• Dissertation

Rights statement

• In Copyright