探討二十二碳六烯酸對人類乳癌細胞株脂肪酸合成酶調控路徑與增生之影響

Abstract

脂肪酸合成酶(Fatty acid synthase，FASN)是參與脂肪酸新生(de novo fatty acid synthesis)的重要酵素，目的將糖解作用的產物乙烯輔酶A合成細胞膜中磷脂質的脂肪酸來源，以促進細胞的增生，因此在乳癌細胞中具有高量的表現。在過去研究中已發現，二十二碳六烯酸(Docosahexaenoic acid，DHA)具有抑制乳癌細胞增生的能力，但詳細機制尚被建立。本實驗假設DHA可透過抑制脂肪酸合成酶及其調控路徑來抑制MCF-7的增生作用。人類乳癌細胞MCF-7培養在DHA中 48小時後，分別加入雌二醇及胰島素刺激1小時及24小時，結果發現，在單純加入DHA後，可使AKT及S6磷酸化下降、Sterol regulatory element binding protein precursor form(SREBP1(P))、mature form(SREBP1(M))及FASN蛋白質表現下降，並且使MCF-7增生現象下降，而在給予E2及insulin刺激後，AKT及S6磷酸化上升，SREBP1(P)、SREBP1(M)及FASN蛋白質表現增加，並且使MCF-7增生現象上升，而給予DHA則可抑制其作用；在E2及insulin的刺激下給予PI3K inhibitorLY294002後，發現AKT及S6的磷酸化下降、SREBP1(P)、SREBP1(M)及FASN的蛋白表現下降，而同時加入LY294002及DHA後，DHA可以加強LY294002抑制AKT的磷酸化、SREBP1(P)、SREBP1(M)及FASN的蛋白表現；在E2及insulin的刺激下給予mTOR inhibitor Rapamycin後，發現S6的磷酸化下降，AKT的磷酸化上升、SREBP1(P)及SREBP1(M)的蛋白質表現不受影響，FASN的蛋白質表現則上升，而同時加入DHA及Rapamycin後，DHA可加強Rapamycin抑制S6的磷酸化作用，並且AKT的磷酸化、SREBP1及FASN的蛋白質表現下降。綜合以上結果，DHA能夠抑制AKT和S6的磷酸化、SREBP1(P)、SREBP1(M)及FASN的蛋白質表現量，並且能使MCF-7細胞增生下降，而在E2及insulin的刺激下，DHA亦能抑制其效果。

Fatty acid synthase (FASN), the major enzyme for de novo fatty acid synthesis, is highly expressed in the cancer cells. Docosahexaenoic acid (DHA, 22:6n-3) is found to inhibit proliferation of breast cancer cells, but the mechanism is not clear. We then examined the effects of DHA on regulation of FASN expression and proliferation in human breast cancer MCF-7cells. Cells were pretreated with 60 uM DHA, arachidonic acid (AA, 20:4n-6) and oleic acid (OA, 18:1n-9) for 48hrs, and then were stimulated without or with estradiol (E2) or insulin. Supplementation of DHA but not AA and OA decreased the expression of SREBP1 precursor and mature form and FASN. E2 and insulin stimulation increased but DHA decreased the expression of pAKT/AKT, pS6/S6, SREBP1and FASN, and cell proliferation. In addition, DHA enhanced the inhibiting of LY294002 on pAKT signaling for the SREBP1and FASN expression. However, by adding rapamycin, an inhibitor of m-TOR signaling pS6/S6, the FASN expression was increased. We concluded that DHA inhibit pAKT signaling for the expression of SREBP1 and FASN and cell proliferation in MCF-7.