Bi-allelic Alteration and Dysregulation of the Hippo Pathway in Mucinous Tubular and Spindle Cell Carcinoma of the Kidney

Mucinous tubular and spindle cell carcinoma (MTSCC) is a relatively rare subtype of renal cell carcinoma with distinctive morphologic and cytogenetic features. Here we carry out whole exome and transcriptome sequencing of a multi-institutional cohort of MTSCC (n=22). We demonstrate the presence of either biallelic loss of Hippo pathway tumor suppressor genes (TSGs) and/or evidence of alteration of Hippo pathway genes in 85% of samples.  PTPN14 (31%) and NF2 (22%) were the most commonly implicated Hippo pathway genes while other genes such as SAV1 and HIPK2 were also involved in a mutually exclusive fashion.  Mutations in the context of recurrent chromosomal losses amounted to bi-allelic alterations in these TSGs. As a read-out of Hippo pathway inactivation, a majority of cases (90%) exhibited increased nuclear YAP1 protein expression. To identify transcriptional targets of the Hippo pathway in kidney we performed PTPN14 knockdown followed by RNA-seq in 2 kidney cancer cell lines (CAKI-1 and A-704) and a normal kidney epithelial cell line (HK-2). PTPN14 siRNAs were first functionally validated in a MCF-7 TEAD reporter luciferase stable cell line. Both siRNAs showed comparable knockdown efficiency and significantly increased luciferase reporter activity. In 2 of the kidney cell lines PTPN14 knockdown increased cell proliferation compared to non-target controls. While we observed excellent correlation between genes dysregulated by either PTPN14 or LATS1 knockdown within each cell line (HK2, CAKI-1 and A704), the overlap across the 3 cell lines was only 23 genes. Further, these 23 genes did not show concordant differential expression in MTSCC tumors. Overall, these results illustrate the marked tissue specificity of Hippo pathway targets.Finally, taken together, nearly all cases of MTSCC exhibit some evidence of Hippo pathway dysregulation. Overall design: Cell lines (CAKI-1, HK2 or A704) were either transfected with 2 independent siRNAs or non-target controls. Forty eight hours post transcription total RNA was isolated and subjected to RNA-seq analysis

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Mehra R, Vats P, Cieslik M, Cao X, Su F, Shukla S, Udager AM, Wang R, Pan J, Kasaian K, Lonigro R, Siddiqui J, Premkumar K, Palapattu G, Weizer A, Hafez KS, Wolf JS Jr, Sangoi AR, Trpkov K, Osunkoya AO, Zhou M, Giannico G, McKenney JK, Dhanasekaran SM, Chinnaiyan AM