GPNMB expression identifies TSC1/2/mTOR‐associated and MiT family translocation‐driven renal neoplasms

Abstract

GPNMB (Glycoprotein nonmetastatic B) and other TFE3/TFEB transcriptional targets have been proposed as markers for MiT translocation renal cell carcinomas (tRCC). We recently demonstrated that constitutive mTORC1 activation via TSC1/2 loss leads to increased activity of TFE3/TFEB, suggesting that the pathogenesis and molecular markers for tRCC and TSC1/2-associated tumors may be overlapping. We examined GPNMB expression in human kidney and angiomyolipoma (AML) cell lines with TSC2 and/or TFE3/TFEB loss produced using CRISPR-Cas9 genome editing as well as in a mouse model of Tsc2 inactivation-driven renal tumorigenesis. Using an automated immunohistochemistry (IHC) assay for GPNMB, digital image analysis was employed to quantitatively score expression in clear cell RCC (ccRCC, n=87), papillary RCC (papRCC, n=53), chromophobe RCC (chRCC, n=34), oncocytoma (n=4), TFE3- or TFEB-driven tRCC (n=56), eosinophilic solid and cystic RCC (ESC, n=6), eosinophilic vacuolated tumor (EVT, n=4) and low grade oncocytic tumor (LOT, n=3) as well as AML (n=29) and PEComa (n=8). In cell lines, GPNMB was up-regulated following TSC2 loss in a MiT/TFE- and mTORC1-dependent fashion. Renal tumors in Tsc2+/- A/J mice showed upregulation of GPNMB compared to normal kidney. Mean GPNMB expression was significantly higher in tRCC compared to ccRCC (pTSC1/2/MTOR alteration-associated renal tumors (including ESC, LOT, AML and PEComa) was comparable to that in tRCC. The immunophenotype of tRCC and TSC1/2/MTOR alteration-associated renal tumors is highly overlapping, likely due to the increased activity of TFE3/TFEB in both, revealing an important caveat regarding the use of TFE3/TFEB-transcriptional targets as diagnostic markers.