The Role of CTHRC1 in the Pathogenesis of LAM

Lymphangioleiomyomatosis (LAM) is a cystic lung disease which primarily affects women of childbearing age, with rapid progression during pregnancy. LAM is a manifestation of tuberous sclerosis complex (TSC), a hereditary disease caused by mutational inactivation of the TSC1 or TSC2 tumor suppressor genes.

Collagen triple helix repeat containing 1 (CTHRC1) is a secreted protein that is highly expressed in many cancers and associated with poor prognosis. CTHRC1 is implicated in tumor cell proliferation and invasion in several cancers.

We discovered a 10-fold increase of CTHRC1 expression in LAM patient-derived angiomyolipoma tissue compared to controls (p<0.0001). CTHRC1 is also elevated in cellular models of TSC, including Tsc1 and Tsc2-deficient mouse embryonic fibroblast (MEFs), and TSC2-deficient LAM patient-derived cells, relative to controls (~6-60-fold, p<.05). Furthermore, Cthrc1 mRNA is elevated ~250 fold (P < 0.0001) in kidney tissue from a ROSACreERT2 TSC2 mouse model. Cthrc1 knockdown decreases proliferation (~2.5-fold, P < 0.0001) and colony formation (~7-fold, P < 0.0001) in Tsc2-null cells, with no effect on TSC2-expressing cells. Transcription factors EB and E3 (TFEB/TFE3) are master coordinators of lysosomal biogenesis and autophagy; their transcriptional activity is hyperactivated in LAM. TFEB/TFE3 recognize a promoter sequence termed the CLEAR motif. CTHRC1 contains six CLEAR motifs upstream of its transcriptional start site. Importantly, CTHRC1 mRNA and protein expression are decreased by TFE3 knockdown in Tsc1 and Tsc2-null MEFs (~2-fold, p < 0.0001) and by TFEB knockdown in 621-102 cells (~2.5-fold, p < 0.01). Taken together, our results indicate CTHRC1 is upregulated in LAM via increased TFEB and TFE3 transcriptional activity; establishing for the first time that CTHRC1 is a TFEB/TFE3 target, and that CTHRC1 promotes cell proliferation.