Recombinant Tumor Suppressor TSC1 Differentially Interacts with Escherichia coli DnaK and Human HSP70

Impact of Co-chaperones and Posttranslational Modifications Toward Hsp90 Drug Sensitivity

Posttranslational modifications (PTMs) regulate myriad cellular processes by modulating protein function and protein-protein interaction. Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone whose activity is responsible for the stabilization and maturation of more than 300 client proteins. Hsp90 is a substrate for numerous PTMs, which have diverse effects on Hsp90 function. Interestingly, many Hsp90 clients are enzymes that catalyze PTM, demonstrating one of the several modes of regulation of Hsp90 activity. Approximately 25 co-chaperone regulatory proteins of Hsp90 impact structural rearrangements, ATP hydrolysis, and client interaction, representing a second layer of influence on Hsp90 activity. A growing body of literature has also established that PTM of these co-chaperones fine-tune their activity toward Hsp90; however, many of the identified PTMs remain uncharacterized. Given the critical role of Hsp90 in supporting signaling in cancer, clinical evaluation of Hsp90 inhibitors is an area of great interest. Interestingly, differential PTM and co-chaperone interaction have been shown to impact Hsp90 binding to its inhibitors. Therefore, understanding these layers of Hsp90 regulation will provide a more complete understanding of the chaperone code, facilitating the development of new biomarkers and combination therapies.

Emerging Link between Tsc1 and FNIP Co-Chaperones of Hsp90 and Cancer

Heat shock protein-90 (Hsp90) is an ATP-dependent molecular chaperone that is tightly regulated by a group of proteins termed co-chaperones. This chaperone system is essential for the stabilization and activation of many key signaling proteins. Recent identification of the co-chaperones FNIP1, FNIP2, and Tsc1 has broadened the spectrum of Hsp90 regulators. These new co-chaperones mediate the stability of critical tumor suppressors FLCN and Tsc2 as well as the various classes of Hsp90 kinase and non-kinase clients. Many early observations of the roles of FNIP1, FNIP2, and Tsc1 suggested functions independent of FLCN and Tsc2 but have not been fully delineated. Given the broad cellular impact of Hsp90-dependent signaling, it is possible to explain the cellular activities of these new co-chaperones by their influence on Hsp90 function. Here, we review the literature on FNIP1, FNIP2, and Tsc1 as co-chaperones and discuss the potential downstream impact of this regulation on normal cellular function and in human diseases.

An Insight of Scientific Developments in TSC for Better Therapeutic Strategy

Tuberous sclerosis complex (TSC) is a rare genetic disease, which is characterized by noncancerous tumors in multi-organ systems in the body. Mutations in the TSC1 or TSC2 genes are known to cause the disease. The resultant mutant proteins TSC1 (hamartin) and TSC2 (tuberin) complex evade its normal tumor suppressor function, which leads to abnormal cell growth and proliferation. Both TSC1 and TSC2 are involved in several protein-protein interactions, which play a significant role in maintaining cellular homeostasis. The recent biochemical, genetic, structural biology, clinical and drug discovery advancements on TSC give a useful insight into the disease as well as the molecular aspects of TSC1 and TSC2. The complex nature of TSC disease, a wide range of manifestations, mosaicism and several other factors limits the treatment choices. This review is a compilation of the course of TSC, starting from its discovery to the current findings that would take us a step ahead in finding a cure for TSC.