Biology subjects

Makena, M. R.

Publications and source records attributed to Makena, M. R..

6 recordsLinked to original sources

bioRxiv2023

The Endosomal pH Regulator NHE6 is Required for Insulin-Stimulated Glucose Uptake in Adipocytes

ObjectiveTrafficking of GLUcose Transporter isoform 4 (GLUT4) from the adipocyte vesicular pool to the cell surface is tightly regulated by insulin to maintain glucose homeostasis in response to changing demands in energy consumption. Previously, endosomal Na+/H+ exchanger 6 (NHE6, gene name SLC9A6) was identified in adipocyte plasma membranes and shown to associate with GLUT4-positive vesicles. However, the functional contribution of NHE6 to GLUT4 trafficking and glucose uptake remained uncharacterized. MethodsNHE6 was knocked down in 3T3L1 cells either before or after differentiation into adipocytes using lentiviral delivery of shRNA. Uptake of [3H] 2-deoxyglucose into adipocytes was quantified in response to insulin. We used epitope tagged constructs to distinguish between localization of vesicular and surface levels of NHE6 and GLUT4 proteins. Protein and transcript levels of components of the glucose signaling pathway were monitored by qPCR and Western analysis, respectively, in response to NHE6 knockdown and/or treatment with chemical modulators of endosomal pH. ResultsWe show that insulin-stimulated glucose uptake in adipocytes is severely impaired upon NHE6 depletion. Correspondingly, insulin-stimulated surface expression of GLUT4 at the adipocyte plasma membrane was diminished in NHE6 knockdown cells due to a post-transcriptional decrease in basal GLUT4. Metformin response of GLUT4 was also muted in the absence of NHE6. Further, we demonstrate diminished activation of the GLUT4 translocation pathway in the absence of NHE6 via reduced expression of the insulin receptor and reduced phosphorylation of the downstream effector kinase Akt. Components of GLUT4 storage vesicles, including GLUT4, LRP1 and sortilin were downregulated in NHE6-knockdown adipocytes under basal conditions. Proteostatic control of key components of the insulin signaling pathway (insulin receptor, GLUT4) could be restored by chemical bypass of NHE6 using the V-ATPase inhibitor bafilomycin or the Na+/H+ exchanger mimetic monensin. ConclusionsThus, NHE6 is critical for proper expression and trafficking of GLUT4. Basal expression of both insulin receptor and GLUT4 in NHE6 knockdown cells could be restored by bafilomycin-inhibition of the H+-ATPase or the H+ ionophore monensin pointing to pH dysregulation as the underlying defect. We suggest that NHE6 is a component of GLUT4 storage vesicles where it regulates proteostasis. These findings establish NHE6 as a novel contributor to glucose homeostasis and energy metabolism with implications for Christianson syndrome patients who carry loss of function mutations in the SLC9A6 gene. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/551163v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@f6fc88org.highwire.dtl.DTLVardef@13d7faforg.highwire.dtl.DTLVardef@89d577org.highwire.dtl.DTLVardef@11da50a_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2021

The Endosomal pH Regulator NHE9 is a Driver of Stemness in Glioblastoma

A small population of self-renewing stem cells initiate tumors and maintain therapeutic resistance in glioblastoma. Given the limited treatment options and dismal prognosis for this disease there is urgent need to identify drivers of stem cells that could be druggable targets. Previous work showed that the endosomal pH regulator NHE9 is upregulated in glioblastoma and correlates with worse survival prognosis. Here, we probed for aberrant signaling pathways in patient-derived glioblastoma cells and found that NHE9 increases cell surface expression and phosphorylation of multiple receptor tyrosine kinases by promoting their escape from lysosomal degradation. Downstream of NHE9-mediated receptor activation, oncogenic signaling pathways converged on the JAK2-STAT3 transduction axis to induce pluripotency genes Oct4 and Nanog and suppress markers of glial differentiation. We used both genetic and chemical approaches to query the role of endosomal pH in glioblastoma phenotypes. Loss-of-function mutations in NHE9 that failed to alkalinize endosomal lumen did not increase self-renewal capacity of gliomaspheres in vitro. However, monensin, a chemical mimetic of Na+/H+ exchanger activity, and the H+ pump inhibitor bafilomycin bypassed NHE9 to directly alkalinize the endosomal lumen resulting in stabilization of receptor tyrosine kinases and induction of Oct4 and Nanog. Using orthotopic models of primary glioblastoma cells we found that NHE9 increased tumor initiation in vivo. We propose that NHE9 initiates inside-out signaling from the endosomal lumen, distinct from the established effects of cytoplasmic and extracellular pH on tumorigenesis. Endosomal pH may be an attractive therapeutic target that diminishes stemness in glioblastoma, agnostic of specific receptor subtype. SignificanceA well-known hallmark of cancer is excessive acidification of tumor microenvironment, caused by upregulation of Na+/H+ exchanger activity on the cancer cell membrane. However, the role of organellar pH in tumor biology has not been established. This study identifies a mechanistic link between upregulation of the endosomal Na+/H+ exchanger NHE9 and stemness properties in glioblastoma, the most malignant and common brain tumor in adults. By increasing pH of the recycling endosome, NHE9 exerts a broad effect on post-translational stability and activation of multiple receptor tyrosine kinases, leading to increased stem cell-like properties of self-renewal and tumor initiation in glioblastoma models. Our findings suggest that targeting NHE9 or endosomal pH could be an effective strategy for receptor agnostic glioblastoma treatment.

cancer biology↗

bioRxiv2021

ALT Neuroblastoma Chemoresistance due to ATM Activation by Telomere Dysfunction is Reversible with the ATM Inhibitor AZD0156

Cancers overcome replicative immortality by activating either telomerase or an alternative lengthening of telomeres (ALT) mechanism. ALT occurs in [~] 25% of high-risk neuroblastomas and relapse or progression in ALT neuroblastoma patients during or after front-line therapy is frequent and almost uniformly fatal. Temozolomide + irinotecan is commonly used as salvage therapy for neuroblastoma. Patient-derived cell-lines and xenografts established from relapsed ALT neuroblastoma patients demonstrated de novo resistance to temozolomide + irinotecan (as SN-38 in vitro, P<0.05) and in vivo (mouse event-free survival (EFS) P<0.0001) relative to telomerase-positive neuroblastomas. We observed that ALT neuroblastoma cells manifest constitutive ATM kinase activation due to spontaneous telomere dysfunction while telomerase- positive tumors lacked constitutive ATM activation or spontaneous telomere DNA damage. We demonstrated that induction of telomere dysfunction resulted in ATM activation that in turn conferred resistance to temozolomide + SN-38 (4.2 fold-change in IC50, P<0.001). ATM kinase shRNA knock-down or inhibition using a clinical-stage small molecule inhibitor (AZD0156) reversed resistance to temozolomide + irinotecan in ALT neuroblastoma cell-lines in vitro (P<0.001) and in 4 ALT xenografts in vivo (EFS P<0.0001). AZD0156 showed modest to no enhancement of temozolomide + irinotecan activity in telomerase-positive neuroblastoma cell lines and xenografts. ATR inhibition using AZD6738 did not enhance temozolomide + SN-38 activity in ALT neuroblastoma cell lines. Thus, resistance to chemotherapy in ALT neuroblastoma occurs via ATM kinase activation and was reversed with the ATM inhibitor AZD0156. Combining AZD0156 with temozolomide + irinotecan warrants clinical testing in neuroblastoma. One Statement SummaryATM activation at telomeres confers resistance to DNA damaging chemotherapy in ALT neuroblastoma that was reversed with ATM knockdown or inhibition.

cancer biology↗

bioRxiv2020

Epigenetic Modulation of SPCA2 Reverses Epithelial to Mesenchymal Transition in Breast Cancer Cells

The secretory pathway Ca2+-ATPase SPCA2 is a tumor suppressor in triple receptor negative breast cancer (TNBC), a highly aggressive molecular subtype that lacks tailored treatment options. Low expression of SPCA2 in TNBC confers poor survival prognosis in patients. Previous work has established that re-introducing SPCA2 to TNBC cells restores basal Ca2+ signaling, represses mesenchymal gene expression, mitigates tumor migration in vitro and metastasis in vivo. In this study, we examined the effect of histone deacetylase inhibitors (HDACi) in TNBC cell lines. We show that the pan-HDACi vorinostat and the class I HDACi romidepsin induce dose-dependent upregulation of SPCA2 transcript with concurrent downregulation of mesenchymal markers and tumor cell migration characteristic of epithelial phenotype. Silencing SPCA2 abolished the ability of HDACi to reverse epithelial to mesenchymal transition (EMT). Independent of ATPase activity, SPCA2 elevated resting Ca2+ levels to activate downstream components of non-canonical Wnt/Ca2+ signaling. HDACi treatment led to SPCA2-dependent phosphorylation of CAMKII and {beta}-catenin, turning Wnt signaling off. We conclude that SPCA2 mediates the efficacy of HDACi in reversing EMT in TNBC by a novel mode of non-canonical Wnt/Ca2+ signaling. Our findings provide incentive for screening epigenetic modulators that exploit Ca2+ signaling pathways to reverse EMT in breast tumors. Simple SummaryThe triple receptor negative breast cancer subtype, or TNBC, currently has no tailored treatment options. TNBC is highly metastatic, associated with high patient mortality, and disproportionately occurs in Black/African American women where it contributes to racial disparities in health outcomes. Therefore, we focused on new therapeutic approaches to TNBC. We discovered that levels of the Calcium-ATPase SPCA2 are abnormally low in TNBC and that these low levels correlate with poor survival prognosis in patients. Previously, we showed that recombinant SPCA2 prevented TNBC cells from acquiring aggressive mesenchymal properties associated with metastasis both in vitro and in vivo. These findings motivated us to search for drugs that turn the SPCA2 gene back on in TNBC cells. In this study, we show that histone deacetylase inhibitors increase SPCA2 levels, activate Ca2+ signaling and convert cancer cells to a less aggressive epithelial state. These findings could lead to new treatment options for TNBC. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=140 HEIGHT=200 SRC="FIGDIR/small/379685v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@13b2565org.highwire.dtl.DTLVardef@14317forg.highwire.dtl.DTLVardef@1bdbd34org.highwire.dtl.DTLVardef@1d0bd83_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2020

Store Independent Ca2+ Entry Regulates the DNA Damage Response in Breast Cancer Cells

Although the mainstay of treatment for hormone responsive breast tumors is targeted endocrine therapy, many patients develop de novo or acquired resistance and are treated with chemotherapeutic drugs. The vast majority (80%) of estrogen receptor positive tumors also express wild type p53 protein that is a major determinant of the DNA damage response. Tumors that are ER+ and p53WT respond poorly to chemotherapy, although the underlying mechanisms are not completely understood. We describe a novel link between store independent Ca2+ entry (SICE) and resistance to DNA damaging drugs, mediated by the secretory pathway Ca2+-ATPase, SPCA2. In luminal ER+/PR+ breast cancer subtypes, SPCA2 levels are high and correlate with poor survival prognosis. Independent of ion pump activity, SPCA2 elevates baseline Ca2+ levels through SICE and drives cell proliferation. Attenuation of SPCA2 or depletion of extracellular Ca2+ increased mitochondrial ROS production, DNA damage and activation of the ATM/ATR-p53 axis leading to G0/G1 phase cell cycle arrest and apoptosis. Consistent with these findings, SPCA2 knockdown confers chemosensitivity to DNA damaging agents including doxorubicin, cisplatin and ionizing radiation. We conclude that elevated SPCA2 expression in ER+ p53WT breast tumors drives pro-survival and chemotherapy resistance by suppressing the DNA damage response. Drugs that target storeindependent Ca2+ entry pathways may have therapeutic potential in treating receptor positive breast cancer.

cancer biology↗

bioRxiv2018

A Moonlighting Role for SPCA2 in E-cadherin Biogenesis and Suppression of Epithelial-Mesenchymal Transition

Progression of benign tumors to invasive, metastatic cancer requires loss of the cell-adhesion protein E-cadherin. Although intensive efforts have focused on gene repression and silencing mutations, much less is known about posttranslational control of E-cadherin expression in cancer. SPCA2 is a secretory pathway Ca2+-ATPase that is down-regulated in metastatic breast cancer. We show that SPCA2 is tightly co-expressed with epithelial signature genes and required for E-cadherin biogenesis and cell surface expression. Unexpectedly, this function is uncoupled from Ca2+ pumping and mediated by binding to E-cadherin. Loss of SPCA2 is sufficient to disrupt cell-cell adhesion in tumorspheres and elicit mesenchymal gene expression through Hippo-YAP signaling. These findings point to a causal link between low SPCA2 levels and the epithelial-mesenchymal transition required for breast cancer metastasis.\n\nHighlightsO_LISPCA2 is an epithelial marker transcriptionally linked to E-cadherin expression\nC_LIO_LILoss of SPCA2 impairs E-cadherin biogenesis independent of Ca2+ pump activity\nC_LIO_LISPCA2 is required for tumorsphere formation and Hippo-YAP signaling to antagonize epithelial-mesenchymal transition\nC_LIO_LIDown-regulation of SPCA2 in metastatic cancers may contribute to malignancy\nC_LI\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=168 SRC=\"FIGDIR/small/379586_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (28K):\norg.highwire.dtl.DTLVardef@6b1e14org.highwire.dtl.DTLVardef@83edbborg.highwire.dtl.DTLVardef@16cbc5corg.highwire.dtl.DTLVardef@1c2752a_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗