Pleiotropic Roles of Calmodulin in the Regulation of KRas and Rac1 GTPases: Functional Diversity in Health and Disease

Regulation of formin INF2 and its alteration in INF2-linked inherited disorders

Formins are proteins that catalyze the formation of linear filaments made of actin. INF2, a formin, is crucial for correct vesicular transport, microtubule stability and mitochondrial division. Its activity is regulated by a complex of cyclase-associated protein and lysine-acetylated G-actin (KAc-actin), which helps INF2 adopt an inactive conformation through the association of its N-terminal diaphanous inhibitory domain (DID) with its C-terminal diaphanous autoinhibitory domain. INF2 activation can occur through calmodulin binding, KAc-actin deacetylation, G-actin binding, or association with the Cdc42 GTPase. Mutations in the INF2 DID are linked to focal segmental glomerulosclerosis (FSGS), affecting podocytes, and Charcot-Marie-Tooth disease, which affects Schwann cells and leads to axonal loss. At least 80 pathogenic DID variants of INF2 have been identified, with potential for many more. These mutations disrupt INF2 regulation, leading to excessive actin polymerization. This in turn causes altered intracellular trafficking, abnormal mitochondrial dynamics, and profound transcriptional reprogramming via the MRTF/SRF complex, resulting in mitotic abnormalities and p53-mediated cell death. This sequence of events could be responsible for progressive podocyte loss during glomerular degeneration in FSGS patients. Pharmacological targeting of INF2 or actin polymerization could offer the therapeutic potential to halt the progression of FSGS and improve outcomes for patients with INF2-linked disease.

KRas4b-Calmodulin Interaction with Membrane Surfaces: Role of Headgroup, Acyl Chain, and Electrostatics

KRas4b is a small plasma membrane-bound G-protein that regulates signal transduction pathways. The interaction of KRas4b with the plasma membrane is governed by both its basic C-terminus, which is farnesylated and methylated, and the lipid composition of the membrane itself. The signaling activity of KRas4b is intricately related to its interaction with various binding partners at the plasma membrane, underlining the critical role played by the lipid environment. The calcium-binding protein calmodulin binds farnesylated KRas4b and plays an important role in the dynamic spatial cycle of KRas4b trafficking in the cell. We utilize Biolayer Interferometry to assay the role of lipid headgroup, chain length, and electrostatics in the dissociation kinetics of fully post-translationally modified KRas4b from Nanodisc bilayers with defined lipid compositions. Our results suggest that calmodulin promotes the dissociation of KRas4b from an anionic membrane, with a comparatively slower displacement of KRas4b from PIP2 relative to PS containing bilayers. In addition to this headgroup dependence, KRas4b dissociation appears to be slower from Nanodiscs wherein the lipid composition contains mismatched, unsaturated acyl chains as compared to lipids with a matched acyl chain length. These findings contribute to understanding the role of the lipid composition in the binding of KRas4b and release from lipid bilayers, showing that the overall charge of the bilayer, the identity of the headgroups present, and the length and saturation of the acyl chains play key roles in KRas4b release from the membrane, potentially providing insights in targeting Ras-membrane interactions for therapeutic interventions.

Methamphetamine Dysregulates Macrophage Functions and Autophagy to Mediate HIV Neuropathogenesis

HIV-neurocognitive impairment (HIV-NCI) can be a debilitating condition for people with HIV (PWH), despite the success of antiretroviral therapy (ART). Substance use disorder is often a comorbidity with HIV infection. The use of methamphetamine (meth) increases systemic inflammation and CNS damage in PWH. Meth may also increase neuropathogenesis through the functional dysregulation of cells that harbor HIV. Perivascular macrophages are long-lived reservoirs for HIV in the CNS. The impaired clearance of extracellular debris and increased release of reactive oxygen species (ROS) by HIV-infected macrophages cause neurotoxicity. Macroautophagy is a vital intracellular pathway that can regulate, in part, these deleterious processes. We found in HIV-infected primary human macrophages that meth inhibits phagocytosis of aggregated amyloid-β, increases total ROS, and dysregulates autophagic processes. Treatment with widely prescribed ART drugs had minimal effects, although there may be an improvement in phagocytosis when co-administered with meth. Pharmacologically inhibited lysosomal degradation, but not induction of autophagy, further increased ROS in response to meth. Using mass spectrometry, we identified the differentially expressed proteins in meth-treated, HIV-infected macrophages that participate in phagocytosis, mitochondrial function, redox metabolism, and autophagy. Significantly altered proteins may be novel targets for interventional strategies that restore functional homeostasis in HIV-infected macrophages to improve neurocognition in people with HIV-NCI using meth.

Upregulation of the Mevalonate Pathway through EWSR1-FLI1/EGR2 Regulatory Axis Confers Ewing Cells Exquisite Sensitivity to Statins

Ewing sarcoma (EwS) is an aggressive primary bone cancer in children and young adults characterized by oncogenic fusions between genes encoding FET-RNA-binding proteins and ETS transcription factors, the most frequent fusion being EWSR1-FLI1. We show that EGR2, an Ewing-susceptibility gene and an essential direct target of EWSR1-FLI1, directly regulates the transcription of genes encoding key enzymes of the mevalonate (MVA) pathway. Consequently, Ewing sarcoma is one of the tumors that expresses the highest levels of mevalonate pathway genes. Moreover, genome-wide screens indicate that MVA pathway genes constitute major dependencies of Ewing cells. Accordingly, the statin inhibitors of HMG-CoA-reductase, a rate-limiting enzyme of the MVA pathway, demonstrate cytotoxicity in EwS. Statins induce increased ROS and lipid peroxidation levels, as well as decreased membrane localization of prenylated proteins, such as small GTP proteins. These metabolic effects lead to an alteration in the dynamics of S-phase progression and to apoptosis. Statin-induced effects can be rescued by downstream products of the MVA pathway. Finally, we further show that statins impair tumor growth in different Ewing PDX models. Altogether, the data show that statins, which are off-patent, well-tolerated, and inexpensive compounds, should be strongly considered in the therapeutic arsenal against this deadly childhood disease.

An emerging role of KRAS in biogenesis, cargo sorting and uptake of cancer-derived extracellular vesicles

Extracellular vesicles (EVs) are nanovesicles secreted for intercellular communication with endosomal network regulating secretion of small EVs (or exosomes) that play roles in cancer progression. As an essential oncoprotein, Kirsten rat sarcoma virus (KRAS) is tightly regulated by its endosomal trafficking for membrane attachment. However, the crosstalk between KRAS and EVs has been scarcely discussed despite its endocytic association. An overview of the oncogenic role of KRAS focusing on its correlation with cancer-associated EVs should provide important clues for disease prognosis and inspire novel therapeutic approaches for treating KRAS mutant cancers. Therefore, this review summarizes the relevant studies that provide substantial evidence linking KRAS mutation to EVs and discusses the oncogenic implication from the aspects of biogenesis, cargo sorting, and release and uptake of the EVs.

Effect of Electro-acupuncture on Vasomotor Symptoms in Rats with Acute Cerebral Infarction Based on Phosphatidylinositol System

Objective

To investigate the effect of electro-acupuncture (EA) on vasomotor symptoms in rats with acute cerebral infarction, by observing the changes in the expression of factors related to the phosphatidylinositol (PI) system.

Methods

Forty-two Wistar rats were randomly divided into 3 groups by a random number table: the control group (n=6), the model group (n=18) and the EA group (n=18). The EA group was given EA treatment at Shuigou (GV 26) instantly after modeling with middle cerebral artery occlusion (MCAO) method, while the model and control groups were not given any treatment. The degrees of neurological deficiency were evaluated using neurological severity scores (NSS) and the brain blood flow was evaluated by a laser scanning confocal microscope. Western blot analysis was conducted to detect the expression levels of G-protein subtype (Gq) and calmodulin (CaM). Competition for protein binding was conducted to detect the expression level of inositol triphosphate (IP3). Thin layer quantitative analysis was conducted to detect the expression level of diacylglycerol (DAG). The expression level of intracellular concentration of free calcium ion ([Ca²⁺]_i) was detected by flow cytometry.

Results

The NSS of the model group was significantly higher than the control group at 3 and 6 h after MCAO (P<0.01), while the EA group was significantly lower than the model group at 6 h (P<0.01). The cerebral blood flow in the model group was significantly lower than the control group at 1, 3 and 6 h after MCAO (P<0.01), while for the EA group it was remarkably higher than the model group at the same time points (P<0.01). The expressions of Gq, CaM, IP3, DAG and [Ca²⁺]_i in the model group were significantly higher than the control group (P<0.05 or P<0.01), and those in the EA group were significantly lower than the model group at the same time points (P<0.05 or P<0.01).

Conclusion

EA treatment at GV 26 can effectively decrease the over-expression of related factors of PI system in rats with acute cerebral infarction, improve cerebral autonomy movement, and alleviate cerebral vascular spasm.

Effect of PLC-β1/CaM signaling pathway mediated by AT1R on the occurrence and development of hepatocellular carcinoma

Objective

To study the roles of AT1R, PLC-β1, CaM and other related signal molecules in the formation and development of hepatocellular carcinoma (HCC) and their correlation.

Methods

ELISA and immunohistochemistry were used to analyze the expressions of target proteins in serum and liver tissue of HCC patients, and the correlation between AT1R, PLC-β1 and CaM and postoperative survival status of patients was followed up and determined. CCK-8 method was used to screen the doses of Ang II and candesartan sensitive to HepG2 and HCCLM3 cells. Transwell experiment was used to observe the effects of different drugs on the migration and invasion activity of HCC cells. Meanwhile, flow cytometry and Western blot were used to detect the expression levels of AT1R, PLC-β1 and CaM in the cells. Then PLC-β1 siRNA was selected to transfect HCC cells, so as to further clarify the mechanism of the above signal proteins. HepG2 cells were inoculated under the hepatic capsule of mice to induce the formation of HCC in situ. Ang II and candesartan were used to stimulate HCC mice to observe the difference in liver appearance and measure the liver index. Finally, ELISA and immunofluorescence experiments were selected to analyze the levels of target proteins in mouse serum and liver tissue.

Results

The expression levels of target proteins in serum and liver tissue of HCC patients were significantly increased, and the postoperative survival time of patients with high expression of AT1R, PLC-β1 or CaM was obviously shortened. Ang II and candesartan could significantly promote and inhibit the motility of HCC cells, and had different effects on the levels of AT1R, PLC-β1 and CaM in cells. However, in hepatocellular carcinoma cells transfected with PLC-β1 siRNA, the intervention ability of drugs was obviously weakened. Ang II could significantly promote the formation and progression of mouse HCC, while candesartan had the opposite effect. Meanwhile, medications could affect the expressions of target proteins in mouse serum and liver tissue.

Conclusion

AT1R, PLC-β1 and CaM may be risk factors affecting the formation and prognosis of HCC, and the PLC-β1/CaM signaling pathway mediated by AT1R is an important way to regulate the migration and invasion activity of HCC cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02261-8.

The dynamic nature of the K-Ras/calmodulin complex can be altered by oncogenic mutations

Oncogenic mutant K-Ras promotes cancer cell proliferation, migration, invasion, and survival by assembling signaling complexes. To date, the functional and structural roles of K-Ras mutations within these complexes are incompletely understood despite their mechanistic and therapeutic significance. Here, we review recent advances in understanding specific binding between K-Ras and the calcium sensor calmodulin. This interaction positively and negatively regulates diverse functions of K-Ras in cancer, suggesting flexibility in K-Ras/calmodulin complex formation. Also, structural data suggest that oncogenic K-Ras likely samples several conformational states, influencing its distinct assemblies with calmodulin and with other proteins. Understanding how K-Ras interacts with calmodulin and with other partners is essential to discovering novel inhibitors of K-Ras in cancer.

Ras-Related C3 Botulinum Toxin Substrate 1 Combining With the Mixed Lineage Kinase 3- Mitogen-Activated Protein Kinase 7- c-Jun N-Terminal Kinase Signaling Module Accelerates Diabetic Nephropathy

Ras-related C3 botulinum toxin substrate 1 (RAC1) activation plays a vital role in diabetic nephropathy (DN), but the exact mechanism remains unclear. In this study, we attempted to elucidate the precise mechanism of how RAC1 aggravates DN through cellular and animal experiments. In this study, DN was induced in mice by intraperitoneal injection of streptozotocin (STZ, 150mg/kg), and the RAC1 inhibitor NSC23766 was administered by tail vein injection. Biochemical indicators, cell proliferation and apoptosis, and morphological changes in the kidney were detected. The expression of phosphorylated c-Jun N-terminal kinase (p-JNK), nuclear factor-κB (NF-κB), and cleaved caspase-3 and the interaction between RAC1 and the mixed lineage kinase 3 (MLK3)-mitogen-activated protein kinase 7 (MKK7)-JNK signaling module were determined. Furthermore, the colocalization and direct co-interaction of RAC1 and MLK3 were confirmed. Our results showed that RAC1 accelerates renal damage and increases the expression of p-JNK, NF-κB, and cleaved caspase-3. However, inhibition of RAC1 ameliorated DN by downregulating p-JNK, NF-κB, and cleaved caspase-3. Also, RAC1 promoted the assembly of MLK3-MKK7-JNK, and NSC23766 blocked the interaction between RAC1 and MLK3-MKK7-JNK and inhibited the assembly of the MLK3-MKK7-JNK signaling module. Furthermore, RAC1 was combined with MLK3 directly, but the RAC1 Y40C mutant inhibited the interaction between RAC1 and MLK3. We demonstrated that RAC1 combining with MLK3 activates the MLK3-MKK7-JNK signaling module, accelerating DN occurrence and development, and RAC1 Y40 is an important site for binding of RAC1 to MLK3. This study illustrates the cellular and molecular mechanisms of how RAC1 accelerates DN and provides evidence of DN-targeted therapy.

Diverse Roles of Annexin A6 in Triple-Negative Breast Cancer Diagnosis, Prognosis and EGFR-Targeted Therapies

The calcium (Ca2+)-dependent membrane-binding Annexin A6 (AnxA6), is a multifunctional, predominantly intracellular scaffolding protein, now known to play relevant roles in different cancer types through diverse, often cell-type-specific mechanisms. AnxA6 is differentially expressed in various stages/subtypes of several cancers, and its expression in certain tumor cells is also induced by a variety of pharmacological drugs. Together with the secretion of AnxA6 as a component of extracellular vesicles, this suggests that AnxA6 mediates distinct tumor progression patterns via extracellular and/or intracellular activities. Although it lacks enzymatic activity, some of the AnxA6-mediated functions involving membrane, nucleotide and cholesterol binding as well as the scaffolding of specific proteins or multifactorial protein complexes, suggest its potential utility in the diagnosis, prognosis and therapeutic strategies for various cancers. In breast cancer, the low AnxA6 expression levels in the more aggressive basal-like triple-negative breast cancer (TNBC) subtype correlate with its tumor suppressor activity and the poor overall survival of basal-like TNBC patients. In this review, we highlight the potential tumor suppressor function of AnxA6 in TNBC progression and metastasis, the relevance of AnxA6 in the diagnosis and prognosis of several cancers and discuss the concept of therapy-induced expression of AnxA6 as a novel mechanism for acquired resistance of TNBC to tyrosine kinase inhibitors.