Novel Interaction of HSP90 in the Caenorhabditis Elegans Insulin/IGF-1 Signaling Pathway

Background: The insulin/insulin growth factor-1 (IGF-1) signaling (IIS) pathway plays a key role in various processes, primarily, metabolism, growth and development. Though research has elucidated aspects of the IIS pathway, it is not yet fully characterized or understood. A better understanding of the proteins involved in this crucial pathway will provide further insight into disease states such as cancer. Methods: The model organism C. elegans was used due to the strong homology its insulin/IGF-1 receptor shares with that of humans. To identify novel protein interactions with the insulin/IGF-1 receptor, we used a yeast two-hybrid screening protocol, an in vivo approach that closely mimics the cellular environment. After identification of a novel protein interaction with HSP90, we studied the phenotype of C. elegansstrains with a mutant form of HSP90. We hypothesized the physical interaction between HSP90 and the insulin/IGF-1 receptor may stabilize its activity and/or allow it to bind other proteins since HSP90 performs this function when interacting with other proteins. We created a modified yeast two-hybrid screen to identify proteins which interact with the insulin/IGF-1 receptor only in the presence of HSP90. Results: Screening a cDNA library of C. elegans proteins, we found three separate occurrences of interaction with the same protein, the C. elegans homolog of the HSP90 protein. C. elegansstrains with a mutant form of HSP90 showed a similar phenotype to those that have a mutant form of the insulin/IGF-1 receptor, inappropriately entering a developmental stage known as dauer. This strongly suggests HSP90 involvement in the IIS pathway. The modified yeast two-hybrid screen identified 15 interactions, significantly more than with the insulin/IGF-1 receptor alone, supporting the hypothesized stabilizing function of HSP90. Conclusion: Overall, we provide evidence to support a novel protein interaction with the C. elegans insulin/IGF-1 receptor within the IIS pathway. This suggests HSP90 may be a potential target for developing clinical therapies for insulin/IGF-1 receptor related diseases, including cancer and diabetes, two of the leading causes of death in the United States.