SIRT1 is upregulated in cutaneous T-cell lymphoma, and its inhibition induces growth arrest and apoptosis

Abstract

Silent information regulator type-1 (SIRT1) is the best-studied member of the Sirtuin (Sir2) family of nicotinamide dinucleotide (NAD)-dependent class III histone deacetylases (HDACs), but has not yet been explored in cutaneous T-cell lymphoma (CTCL). We analyzed five CTCL cell lines and lesional tissues using flow cytometry, immunostaining, immunoblotting, cell death, viability, and apoptosis assays, small-molecule inhibitors, and shRNA knockdown. We found strong SIRT1 expression among CTCL lines relative to normal lymphocytes. CTCL cells in lesional tissues also expressed SIRT1 strongly. SIRT1 knockdown resulted in reduced cellular metabolism and proliferation, increased apoptosis, and PARP cleavage products. Tenovin-1, which reversibly inhibits class III HDACs (SIRT1 and SIRT2), reduced SIRT enzymatic activity and SIRT1 expression and led to increased apoptosis. These alterations were accompanied by increased forkhead box O3 (FoxO3) in several cell lines and increased nuclear p53, as well as acetylated p53 in wtp53 MyLa CTCL line. A combination of class I/II and class III HDACIs (vorinostat and tenovin-1) produced significantly greater growth inhibition, cell death via apoptosis, as well as superior p53 promoter upregulation in wtp53 MyLa cells as compared with either agent alone. This occurred in a partially p53-dependent manner, as these effects were blunted by p53 knockdown. Our results indicate that SIRT1 is strongly expressed in CTCL. Its inhibition results in reduced growth and increased apoptosis of CTCL cells. Furthermore, our findings suggest that some CTCL patients, such as those with wtp53, might benefit more from treatment with a combination of different classes of HDACIs than with a single agent.

Evidence of an oncogenic role of aberrant TOX activation in cutaneous T-cell lymphoma

“…In 3 CTCL cell lines, TOX suppression by lentivirus-mediated shRNA gene silencing markedly normalized the CTCL cells' resistance to apoptosis and abnormal cell cycle progression, the 2 best-characterized features of CTCL cells. [5][6][7][8] In agreement with in vitro data, subcutaneous injection of CTCL cells into NSG mice confirmed this proliferative disadvantage, in that the ability of TOX-suppressed CTCL cells to induce local tumors was significantly impaired or even abolished. In aggregate, these findings demonstrate the biological importance of sustained TOX activation to the leukemic activities of CTCL cells.…”

“…Although the etiology of CTCL is not yet clear, accumulating evidence indicates that defects in apoptosis and cell cycle control are critical in disease pathogenesis. [5][6][7][8] However, the molecular events leading to these abnormalities have not been well understood. By transcriptome analysis, we have recently demonstrated that the transcript levels of thymocyte selection-associated high-mobility group (HMG) box gene (TOX) are abnormally increased in early-stage MF skin biopsy specimens but not in the biopsy specimens of benign inflammatory dermatoses (BID) or normal skin.…”

Simvastatin attenuates TNF-α-induced apoptosis in endothelial progenitor cells via the upregulation of SIRT1

“…Previous studies have shown that SIRT1 promotes cell survival by repressing p53-dependent apoptosis in response to DNA damage and oxidative stress. This repression occurs via physical interaction with both p53 and the forkhead transcription factor (FOXO) family of proteins (28)(29)(30). Additionally, evidence suggests that SIRT1 may be involved in pathways of telomere maintenance, giving them a putative role in aging and survival (31).…”

Methotrexate and Pralatrexate

“…49 Recent findings showed that the class III HDAC, SIRT1, is overexpressed in CTCL and that its knock-down or inhibition induced growth arrest and apoptosis. 50 31 MTX and PDX are metabolized intracellularly into polyglutamates by folylpolyglutamyl synthetase. 16,32 These polyglutamates are preferentially retained in cells, thereby making them less susceptible to efflux-based drug resistance.…”