Vitamin D3 Induces Autophagy of Human Myeloid Leukemia Cells

Abstract

Vitamin D3 causes potent suppression of various cancer cells; however, significant supraphysiological concentrations of this compound are required for antineoplastic effects. Current combinatorial therapies with vitamin D3 are restricted to differentiation effects. It remains uncertain if autophagy is involved in vitamin D3 inhibition on leukemia cells. Here we show that besides triggering differentiation and inhibiting apoptosis, which was previously known, vitamin D3 triggers autophagic death in human myeloid leukemia cells. Inhibiting differentiation does not efficiently diminish vitamin D3 suppression on leukemia cells. Vitamin D3 up-regulates Beclin1, which binds to class III phosphatidylinositol 3-kinase to trigger autophagy. Vitamin D3 phosphorylates Bad in its BH3 domain, resulting in disassociation of the apoptotic Bad-Bcl-xL complex and association of Bcl-xL with Beclin1 and ultimate suppression of apoptotic signaling. Knockdown of Beclin1 eliminates vitamin D3-induced autophagy and inhibits differentiation but activates apoptosis, suggesting that Beclin1 is required for both autophagy and differentiation, and autophagy cooperates with differentiation but excludes apoptosis, in which Beclin1 acts as an interface for these three different cascades. Moreover, additional up-regulation of autophagy, but not apoptosis, dramatically improves vitamin D3 inhibition on leukemia cells. These findings extend our understanding of the action of vitamin D3 in antineoplastic effects and the role of Beclin1 in regulating multiple cellular cascades and suggest a potentially promising strategy with a significantly better antileukemia effect.1,25-Dihydroxyvitamin D3, the hormonally active form of vitamin D3, plays critical roles in regulating cellular and physiological responses. Treatment of vitamin D3 potently inhibits cell proliferation in a wide range of cancer cells, including myeloid leukemia and carcinomas of the breast, prostate, colon, skin, and brain and inhibits angiogenesis, tumor invasion, and metastases (1-8), suggesting that vitamin D3 has potential applications in cancer prevention and treatment. Vitamin D3 is known to inhibit cancer cell proliferation through the induction of differentiation, which is dependent on the signaling mechanisms involving down-regulation of Akt and its disassociation with Raf1 and subsequent activation of Raf/MEK/ERK 2

Coxiella burnetii modulates Beclin 1 and Bcl-2, preventing host cell apoptosis to generate a persistent bacterial infection

“…Thus, Beclin 1 is a crucial regulator of autophagy and apoptosis in infected cells, because of its role as a member of the Beclin 1/Vps34 complex and its participation in the antiapoptotic complex Beclin 1-Bcl-2, competing with Bad for the binding to Bcl-2. 44 To summarize, the data presented here show that Cb infection is favored by overexpressed Beclin 1 and that depletion of this protein, as well as of the overexpressed Bcl-2, alters the normal development of CRVs. Furthermore, our results suggest the existence of a functional interaction between the autophagic and apoptotic pathways in infected cells, to avoid apoptosis induction and to trigger the autophagy pathway, allowing the survival and development of Cb.…”

“…This notion is supported by results obtained in myeloid leukemia cells, in which the knockdown of Beclin 1 activates apoptosis. 44 These researchers have shown that Beclin 1 acts as a negative regulator of apoptosis because it competes with the pro-apoptotic protein Bad, for binding to the anti-apoptotic protein Bcl-X L , implying that the complex Beclin 1-Bcl-X L has indeed an anti-apoptotic role. 44 In addition, it has recently been reported that dexamethasone induces autophagy in murine T-cell lymphoma line.…”

“…44 These researchers have shown that Beclin 1 acts as a negative regulator of apoptosis because it competes with the pro-apoptotic protein Bad, for binding to the anti-apoptotic protein Bcl-X L , implying that the complex Beclin 1-Bcl-X L has indeed an anti-apoptotic role. 44 In addition, it has recently been reported that dexamethasone induces autophagy in murine T-cell lymphoma line. Furthermore, this autophagy induction is enhanced by Bcl-2 overexpression, apparently because of the inhibition of dexamethasoneinduced apoptosis.…”

Overview of macroautophagy regulation in mammalian cells

“…For example, in HBV (hepatitis B virus)-infected hepatocytes, the HBV x protein increases autophagy by up-regulating the expression of Beclin 1 [160]. In human monocytes and human myeloid leukemia cells, vitamin D3 has been shown to induce autophagy by up-regulating both Beclin 1 and Atg5 [161,162]. The transcription factor implicated has not been identified, but it has been shown that in human monocytes the effect of Vitamin D3 is mediated via cathelicidin.…”

Role of autophagy in the progression and suppression of leukemias

“…Novel anti-cancer therapeutic compounds activating the autophagic pathway are not limited to the species previously stated. In addition to these, (96,97) some derivatives of naphthalimide were found to be potent inhibitors of lymphoid leukemia in murine models [82] while vitamins D3 and K2 were shown to inhibit human myeloid leukemias [83,84]. Glucocorticoids such as dexamethasone also contributed to autophagic death in leukemia of lymphoid origin [85,86].…”