The tumor susceptibility gene TMEM127 is mutated in renal cell carcinomas and modulates endolysosomal function.

TMEM127 is an endosome-associated tumor suppressor gene in pheochromocytomas, neuroendocrine tumors that can co-occur with renal cell carcinomas (RCCs). TMEM127 loss leads to increased mTOR signaling. However, the spectrum of tumors with TMEM127 mutation and how TMEM127 and mTOR interact in tumorigenesis remains unknown. Here, we report that germline TMEM127 mutations occur in RCCs and that some mutant proteins, unlike wild-type (WT) TMEM127, fail to cooperate with activated early endosomal GTPase, Rab5, to inhibit mTOR signaling. Tmem127-null mouse embryonic fibroblasts (MEFs) are deficient in generating early-to-late hybrid endosomes upon constitutive Rab5 activation, a defect rescued by WT, but not mutant, TMEM127. This endosomal dysfunction results in diminished mTOR colocalization with Rab5-positive vesicles. Conversely, active, lysosomal-bound mTOR is increased in Tmem127-null MEFs, which also display enhanced lysosomal biogenesis. Our data map the tumor-suppressive properties of TMEM127 to modulation of mTOR function in the endolysosome, a feature that may contribute to both pheochromocytoma and RCC pathogenesis.

Pheochromocytomas: from genetic diversity to new paradigms.

Pheochromocytomas and paragangliomas are catecholamine-secreting tumors of neural crest origin caused by germline mutations in at least six distinct genes. This genetic heterogeneity has provided a rich source for both the discovery and functional characterization of new tumor-related genes. However, the genetic repertoire of these tumors is still not fully known, and current evidence points to the existence of additional pheochromocytoma susceptibility genes. Here, the unique contributions of three hereditary models of pheochromocytoma that can advance our knowledge of the disease pathogenesis are presented. The first model, loss of succinate dehydrogenase (SDH) function, illustrates how SDHB, C, or D mutations, components of the energy metabolism pathway, serve as a unique system to explore the pervasive metabolic shift of cancer cells towards glycolysis as a source of energy (also known as the Warburg effect) in contrast to the characteristic oxidative phosphorylation of normal cells. In the second model, mechanisms of tumorigenesis distinct from classical pheochromocytoma susceptibility genes are discussed in the context of a novel putative suppressor of neural crest-derived tumors, the KIF1B beta gene. Finally, NF1 loss is highlighted as a valuable study model to investigate the cell lineage selectivity of the Egln3-mediated developmental apoptotic defect of chromaffin precursor cells. Results from these studies may offer clues to understand the tissue specificity of hereditary pheochromocytoma syndromes. These distinct hereditary disease models illustrate how genetic-driven progress has the potential to narrow current gaps in our knowledge of pheochromocytoma and paraganglioma pathogenesis.

Neuron-specific enolase is a useful marker of neuroendocrine origin in pheochromocytoma cell culture

Neuron-specific enolase (NSE) has been used as a marker for neuroendocrine tumors either in immunocytochemical studies or in serum measurements. ln this paper NSE levels were determined in cultured pheochromocytoma cells to test whether it is also a useful marker ín cell culture of tumors derived from neuroendocrine system. Cultured pheochromocytoma cells came from a primary explant and were grown in RPMI supplemented with 20 per cent fetal calf serum, 100 mug/mL ampicillin and 100 mug/mL streptomycin. NSE was measured in culture medium and cell homogenates. Samples from different pheochromocytoma cultures were analyzed and compared to normal cultured fibroblast cells derived from human skin. NSE was measured by a commercially available radioimmunoassay kit. NSE levels were higher in cell homogenates as compared to those in culture medium, reaching levels as high as 6-fold in the former in TE cell line (26.46 ng/mL and 4.39 ng/mL respectively. Serial NSE measurements in culture medium from TE cell line evidenced decreasing values in subsequential subcultures (from 9.24 ng/mL during primary explant to 1.7 ng/ml. in the 10th subculture). In cultured normal fibroblasts, NSE levels in cultured media were definitely lower than those obtained from pheochromocytoma cultures. These preliminary data suggest that NSE may be a useful marker of neuroendocrine derived tumors, such as pheochromocytoma, in culture. Thus, the simplicity and availability of NSE radioimmunoassay provides an alternative to catecholamine measurement to better characterize pheochromocytoma cell lines in culture, with the advantage of faster results at lower costs.