Expression of hexokinase and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase genes in ERN1 knockdown glioma U87 cells: effect of hypoxia and glutamine or glucose deprivation

Abstract

Endoplasmic reticulum stress, as well as hypoxia and ischemia, are important factors for tumor neovascularization and growth. Cancer cells preferentially utilize glycolysis in order to satisfy their increased energetic and biosynthetic requirements. High glucose metabolism of cancer cells is caused by a combination of hypoxia-responsive transcription factors, activation of oncogenic proteins and the loss of tumor suppressor function and is realized in part by activating a family of regulatory bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB) and hexokinase 2. We have studied the effect of hypoxia and ischemia on the expression of PFKFB and hexokinase genes in glioma cell line U87 under knockdown of endoplasmic reticulum-nuclei-1 (ERN1) sensing and signaling enzyme. It was shown that loss of the signaling enzyme ERN1 function leads to an increase in the expression levels of HK1, HK2, PFKFB3 and PFKFB4 mRNA. Moreover, the expression levels of all studied genes increase under hypoxia in control and ERN1-deficient glioma cells; however knockdown of ERN1 suppresses the effect of hypoxia. Besides, HK2 and PFKFB4 are more sensitive to hypoxia than HK1 and PFKFB3. Glucose or glutamine deprivation conditions have different effects on the expression levels of these genes and its effect depends mainly on ERN1 function. Expression levels of alternative splice variants of PFKFB3 and PFKFB4 mRNA change at used experimental conditions in a fashion similar to the basic PFKFB variants. Thus, the expression of hexokinase and PFKFB genes is mainly dependent on ERN1 signaling enzyme function in normal, hypoxic and ischemic conditions.

Endoplasmic reticulum stress, its sensor and signalling systems and the role in regulation of gene expression at malignant tumor growth and hypoxia

“…Таким чином, виключення функції ERN1, основного сенсорно-сигнального ензиму стре-су ендоплазматичного ретикулума, призво-дить до пригнічення росту пухлин і змінює характер гіпоксичної регуляції експресії генів, що контролюють процеси гліколізу, ангіогенезу та проліферації [53,66,67,[71][72][73][77][78][79][80][81]. Залежність гіпоксичної регуляції експресії генів від функції сенсорно-сигнального ензиму ERN1 можна пояснити тим, що ефекти гіпоксії здебільшого опосередковані транскрипційним фактором HIF, а його рівень залежить не лише від рівня кисню, а і від сигнальних шляхів, що опосередковують процеси проліферації, зокре-ма від PI3K (фосфоінозитид-3-кінази), MAPK (протеїнкіназ, що активуються міогеном) та протеїнкінази AKT1 (v-akt murine thymoma viral oncogene homolog 1, що являє собою протеїнкіназу В, PKB) шляхів, які, в свою чер-гу, залежать від сигнального шляху ERN1 [82].…”

Regulation of hexokinase and glucose-6-phosphate dehydrogenase genes expression at norm and pathology

“…Moreover, during its growth a tumor requires the functional signaling system of endoplasmatic reticulum stress as well as hypoxia and ischemia for neovascularization and growth. Therefore, a complete blocking of the ERN1 signal transfer pathway has an antitumor effect [85,86]. The signaling pathway of endoplasmatic reticulum, activated in response to stress-reaction, is conditioned by the process of neovascularization, tumor growth and differentiation as well as death of cells [86].…”