Identification and Functional Characterization of a Novel Germline TMEM127 Mutation in a Rare Co-Occurrence of Familial Pheochromocytoma and Renal Cell Carcinoma

Presentation Number: OR01-6
Date of Presentation: April 3rd, 2017

Yilun Deng*1, Shahida K Flores1, Zi-Ming Cheng1, Yuejuan Qin1, Carl Malchoff2, Robin C. Schwartz2 and Patricia L.M. Dahia1
1UTHSCSA, San Antonio, TX, 2UCONN Health Ctr, FARMINGTON, CT

Abstract

We previously identified the endosomal protein TMEM127 as a tumor suppressor involved in pheochromocytoma susceptibility, and more rarely, in renal cell carcinomas (RCC). Here we describe a patient who developed an epinephrine-secreting pheochromocytoma at age 47 and a left clear-cell renal cell carcinoma (RCC) at 58. Both tumors were surgically removed and the patient shows no signs of recurrence after 18 and 7 years of follow up, respectively. A novel TMEM127 mutation, c.532dupT(p.Y178LfsX48) was detected in germline DNA from the patient and in one sibling with pheochromocytoma. No other mutations were identified by targeted next-generation sequencing of pheochromocytoma susceptibility genes (germline DNA) or cancer genes (pheochromocytoma DNA). Furthermore, no somatic VHL mutations were identified in the RCC, in support of a genetic link between the two tumors in this patient. We previously found that TMEM127 localizes to lysosomal membranes and that its absence or mutation leads to increased activation of mTORC1 signaling. We expressed a GFP-tagged TMEM127_532dupT construct in human kidney 293 (HEK293) cells and found that the mutant displays both punctate and diffuse subcellular distribution, suggesting an intermediate pattern between the punctate wild-type TMEM127 and the diffuse localization seen in early-truncation mutants. We next used CRISPR-Cas9 genome editing to generate HEK293 cells that carry a TMEM127_532dupT mutation. We successfully isolated and sequence-validated multiple clones carrying this mutation. Cells with the TMEM127_ 532dupT mutation exhibited increased activation of mTORC1 downstream targets, recapitulating our earlier findings in TMEM127 mutant or null cells. Finally, to further explore the effects of TMEM127_532dupT on the mTORC1 pathway, we examined this mutant's interaction with components of the protein complex involved in mTORC1 activation. We recently found that TMEM127 associates with the lysosomal component of this complex, LAMTOR1, which is required for full mTORC1 activation. Here, we show that expressed TMEM127_532dupT had markedly deficient binding to LAMTOR1 compared with wild-type TMEM127. These results suggest that TMEM127 may inhibit mTOR signaling by binding to LAMTOR1 and/or other components of the mTORC1 lysosomal complex and that this association is impaired by the 532dupT mutation, which may explain the increased activation of mTORC1 downstream targets detected in the mutant cells. Taken together, our results provide a possible mechanism through which TMEM127 acts as a tumor suppressor. This is only the second report of a co-occurrence of pheochromocytoma and RCC in the same individual with a pathogenic TMEM127 mutation, suggesting that the phenotype related to TMEM127 mutations may include the association between pheochromocytoma and RCC.

 

Nothing to Disclose: YD, SKF, ZMC, YQ, CM, RCS, PLMD