Hyper-activation of mTORC1, a protein kinase downstream of TSC1/2 complex, is the major consequence of tuberous sclerosis complex (TSC) gene mutations. Although drugs that target mTORC1 have been tested for TSC mouse models and clinical trials, it is important to develop alternative strategies for better efficacious treatment of TSC. For this, it is necessary to understand better the contributing factors other than TSC mutations to the development of TSC. TSC-mutated cells show heterogeneity, and other contributing factors in TSC development remain unclear. The TSC disease must depend on other cellular factors for the disease-related symptoms to develop or the severity of the disease states. Amino acid-regulated mTORC1 signaling plays an important role for growth and survival of TSC mutant cells. Amino acids, especially branched chain amino acids, upregulate mTORC1 even in TSC mutant cells. This implies that any mutation that can cause an increase in the amino acid-mTORC1 pathway could contribute positively to TSC development. SH3BP4 has been identified by the Principal Investigator's laboratory as a negative regulator of amino acid-mTORC1 signaling. This gene is deleted in many tumors from patients and thus is a potential tumor suppressor. It is not known whether this gene is mutated in TSC patients. The SH3BP4 gene is located at a locus related to an autism-related region. These results provide a previously unknown link between deregulated amino acid-mTORC1 signaling and growth-related diseases. In this proposed study, we will define the role of SH3BP4 in TSC development and evaluate SH3BP4 as a therapeutic target to suppress TSC. Once our study is successfully completed, the novel target will transform the current therapeutic strategies for TSC. Furthermore, the novel target identified in this study will allow researchers to investigate previously unknown aspects contributing to TSC development.