inositol-1-4-5-trisphosphate and Lymphoma

Autophagy is closely related to tumor cell sensitivity to anticancer drugs. The HDAC (histone deacetylase) inhibitor valproic acid (VPA) interacted synergistically with chemotherapeutic agents to trigger lymphoma cell autophagy, which resulted from activation of AMPK (AMP-activated protein kinase) and inhibition of downstream MTOR (mechanistic target of rapamycin [serine/threonine kinase]) signaling. In an HDAC-independent manner, VPA potentiated the effect of doxorubicin on lymphoma cell autophagy via reduction of cellular inositol 1,4,5 trisphosphate (IP3), blockade of calcium into mitochondria and modulation of PRKAA1/2-MTOR cascade. In murine xenograft models established with subcutaneous injection of lymphoma cells, dual treatment of VPA and doxorubicin initiated IP3-mediated calcium depletion and PRKAA1/2 activation, induced in situ autophagy and efficiently retarded tumor growth. Aberrant genes involving mitochondrial calcium transfer were frequently observed in primary tumors of lymphoma patients. Collectively, these findings suggested an HDAC-independent chemosensitizing activity of VPA and provided an insight into the clinical application of targeting autophagy in the treatment of lymphoma.

Topics: AMP-Activated Protein Kinases; Antineoplastic Agents; Autophagy; Cell Line, Tumor; Drug Synergism; Enzyme Activation; Humans; Inositol 1,4,5-Trisphosphate; Lymphoma; Mitochondria; Signal Transduction; Sirolimus; Valproic Acid

Here, we present evidence that exposure of DT40 lymphoma B cells to low energy electromagnetic field (EMF) results in a tyrosine kinase-dependent activation of phospholipase Cgamma2 (PLC-gamma2) leading to increased inositol phospholipid turnover. B cells rendered PLC-gamma2-deficient by targeted disruption of the PLC-gamma2 gene as well as PLC-gamma2-deficient cells reconstituted with Src homology domain 2 (SH2) domain mutant PLC-gamma2 did not show any increase in inositol-1,4,5-trisphosphate levels after EMF exposure, providing direct evidence that PLC-gamma2 is responsible for EMF-induced stimulation of inositol phospholipid turnover, and its SH2 domains are essential for this function. B cells rendered SYK-deficient by targeted disruption of the syk gene did not show PLC-gamma2 activation in response to EMF exposure. The C-terminal SH2 domain of SYK kinase is essential for its ability to activate PLC-gamma2. SYK-deficient cells reconstituted with a C-terminal SH2 domain mutant syk gene failed to elicit increased inositol phospholipid turnover after EMF exposure, whereas SYK-deficient cells reconstituted with an N-terminal SH2 domain mutant syk gene showed a normal EMF response. LYN kinase is essential for the initiation of this biochemical signaling cascade. Lymphoma B cells rendered LYN-deficient through targeted disruption of the lyn gene did not elicit enhanced inositol phospholipid turnover after EMF exposure. Introduction of the wild-type (but not a kinase domain mutant) mouse fyn gene into LYN-deficient B cells restored their EMF responsiveness. B cells reconstituted with a SH2 domain mutant fyn gene showed a normal EMF response, whereas no increase in inositol phospholipid turnover in response to EMF was noticed in LYN-deficient cells reconstituted with a SH3 domain mutant fyn gene. Taken together, these results indicate that EMF-induced PLC-gamma2 activation is mediated by LYN-regulated stimulation of SYK, which acts downstream of LYN kinase and upstream of PLC-gamma2.

Topics: Animals; B-Lymphocytes; Chickens; Electromagnetic Fields; Enzyme Activation; Enzyme Precursors; Gene Targeting; Inositol 1,4,5-Trisphosphate; Intracellular Signaling Peptides and Proteins; Isoenzymes; Lymphoma; Phosphatidylinositols; Phospholipase C gamma; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-fyn; Signal Transduction; src Homology Domains; src-Family Kinases; Syk Kinase; Type C Phospholipases

Photodynamic therapy (PDT), an experimental cancer treatment employing a photosensitizer and visible light, is a highly efficient inducer of apoptosis (or programmed cell death) in mouse L5178Y lymphoma cells, resulting in extensive DNA fragmentation within 1-2 h. The major targets for PDT are in cellular membranes, and we now find that PDT sensitized by aluminum phthalocyanine causes the rapid (< 1 min) activation of phospholipase C and the breakdown of membrane phosphoinositides, as well as a similarly rapid release of Ca2+ from intracellular pools. A phospholipase C inhibitor, U73122, blocks the rapid transient increases in both inositol-1,4,5-trisphosphate and intracellular Ca2+ levels as well as the subsequent fragmentation of nuclear DNA, whereas the analogue U73343 is much less effective against all of the aforementioned responses. In addition, p-bromphenacyl bromide, an inhibitor of phospholipase A2, blocks DNA fragmentation, and PDT stimulates the release of arachidonic acid, probably by phospholipase A2-dependent breakdown of membrane phospholipids. Thus, photodynamic damage to cell membranes can mimic natural stimuli of phospholipases and initiate apoptosis in L5178Y cells.

Topics: Animals; Apoptosis; Arachidonic Acid; Calcium; Enzyme Activation; Indoles; Inositol 1,4,5-Trisphosphate; Lymphoma; Mice; Organometallic Compounds; Phospholipases A; Phospholipases A2; Photochemotherapy; Tumor Cells, Cultured; Type C Phospholipases