Sphingomyelin synthase 1 suppresses ceramide production and apoptosis post-photodamage

Abstract

The role of sphingomyelin synthase 1 (SMS1), the Golgi membrane isoform of the enzyme, in ceramide metabolism and apoptosis after photodamage with the photosensitizer Pc 4 (PDT) is unclear. In the present study, using electrospray ionization/double mass spectrometry, we show that in Jurkat cells overexpressing SMS1, increases in ceramides were lower than in empty-vector transfectants post-PDT. Similarly, the responses of dihydroceramides and dihydrosphingosine, precursors of ceramide in the de novo synthetic pathway, were attenuated in SMS1-overexpressor after photodamage, suggesting the involvement of the de novo pathway. Overexpression of SMS1 was associated with differential regulation of sphingomyelin levels, as well as with the reduced inhibition of the enzyme post-treatment. Concomitant with the suppressed ceramide response, PDT-induced DEVDase activation was substantially reduced in SMS1-overexpressors. The data show that overexpression of SMS1 is associated with suppressed ceramide response and apoptotic resistance after photodamage.

Tales and Mysteries of the Enigmatic Sphingomyelin Synthase Family

“…Similar to Jurkat cells, 81 over-expression of SMS1 or SMS2 in CHO cells caused an increase of ceramide levels. 77 An increase of ceramide levels was also observed upon down-regulation of either SMS1 or SMS2 in HeLa and Huh cells, 66,72,74 suggesting that changes in ceramide levels due to modulation of SMSs might be differently regulated depending on the specific cellular context.…”

“…81 In these cells, enhanced SMS1 levels caused a general increase of sphingolipids in resting cells. On the other hand, over expression of SMS1 prevented accumulation of ceramide and dihydroceramides following photodamage, as compared to vector control cells, even though no SM accumulation could be observed.…”

Caspase-mediated inhibition of sphingomyelin synthesis is involved in FasL-triggered cell death

“…Total RNA was isolated from Jurkat cells using the Qiagen RNeasy kit and reverse transcribed using oligo(dT) 15 (Promega, Charbonnières, France) and Superscript II (Invitrogen), as recommended by the manufacturers. cDNAs were analyzed by quantitative real-time PCR using specific primers for SMS1, SMS2 and GAPDH (Qiagen) and the Power SYBR Green PCR Master mix (Applied Biosystems, Courtaboeuf, France).…”

“…13 Different stimuli, including TNFa, photodynamic therapy and UVB, have been shown to inhibit de novo SM synthesis. [14][15][16][17] Although homotrimerization of CERT (ceramide transfer protein) has been implicated in UVB-mediated inhibition of SM synthesis, the underlying mechanisms involved are largely unknown. 17 Two different mammalian genes encoding SMS have been cloned so far.…”

“…23 The expression of SMS1 in yeast could limit ceramide accumulation and cell death signaling. 23 Moreover, SMS1 overexpression protected Jurkat cells from phototherapy-induced cell death, 15 whereas SMS1 or SMS2 knockdown sensitized cells. 16 SMS1 overexpression was also partially protective against apoptosis of oligodendroglioma cells triggered by staurosporine.…”