Lymphangioleiomyomatosis (LAM) is a female-predominant cystic lung disease that can lead to respiratory failure. LAM cells typically have inactivating tuberous sclerosis complex 2 (TSC2) mutations and mammalian target of rapamycin (mTOR) complex (mTORC) 1 activation. Clinical response to the mTORC1 inhibitors has been limited, prompting a search for additional therapy for LAM. In this study, we investigated the impact of TSC2 on the expression of poly (ADP-ribose) polymerase (PARP)-1 that initiates the DNA repair pathway, and tested the efficacy of PARP1 inhibitors in the survival of TSC2-deficient (TSC2(-)) cells. We analyzed publicly available expression arrays of TSC2(-) cells and validated the findings using real-time RT-PCR, immunoblotting, and immunohistochemistry. We examined the impact of rapamycin and Torin 1 on PARP1 expression. We also tested the effect of PARP1 inhibitors, 8-hydroxy-2-methylquinazoline-4-one and 3,4-dihydro-5[4-(1-piperindinyl)butoxy]-1(2H)-isoquinoline, on the survival of TSC2(-) cells. We identified the up-regulation of PARP1 in TSC2(-) cells relative to cells in which wild-type TSC2 has been reintroduced (TSC2-addback [TSC2(+)] cells). The transcript levels of PARP1 in TSC2(-) cells were not affected by rapamycin. PARP1 levels were increased in TSC2(-) cells, xenograft tumors of rat-derived TSC2(-) cells, renal cystadenomas from Tsc2(+/-) mice, and human LAM nodules. RNA interference of mTOR failed to reduce PARP1 levels. Proliferation and survival of TSC2(-) cells was reduced in response to PARP1 inhibitor treatment, more so than TSC2(+) cells. TSC2(-) cells exhibit higher levels of PARP1 relative to TSC2(+) cells in an mTOR-insensitive manner. PARP1 inhibitors selectively suppress the growth and induce apoptosis of TSC2(-) cells from patients with LAM. Targeting PARP1 may be beneficial in the treatment of LAM and other neoplasm with mTORC1 activation.
Keywords: lymphangioleiomyomatosis; mammalian target of rapamycin; poly (ADP-ribose) polymerases; rapamycin; tuberous sclerosis complex.