Insulin-induced translocation of IR to the nucleus in insulin responsive cells requires a nuclear translocation sequence

Advances in the role of membrane-bound transcription factors in carcinogenesis and therapy

Protein shuttling between the cytoplasm and nucleus is a unique phenomenon in eukaryotic organisms, integral to various cellular functions. Membrane-bound transcription factors (MTFs), a specialized class of nucleocytoplasmic shuttling proteins, are anchored to the cell membrane and enter the nucleus upon ligand binding to exert their transcriptional regulatory functions. MTFs are crucial in cellular signal transduction, and aberrant nucleocytoplasmic shuttling of MTFs is closely associated with tumor initiation, progression, and resistance to anticancer therapies. Studies have demonstrated that MTFs, such as human epidermal growth factor receptor (HER), fibroblast growth factor receptor (FGFR), β-catenin, Notch, insulin-like growth factor 1 receptor (IGF-1R), and insulin receptor (IR), play critical roles in tumorigenesis and cancer progression. Targeted therapies developed against HERs and FGFRs, among these MTFs, have yielded significant success in cancer treatment. However, the development of drug resistance remains a major challenge. As research on MTFs progress, it is anticipated that additional MTF-targeted therapies will be developed to enhance cancer treatment. In this review, we summarized recent advancements in the study of MTFs and their roles in carcinogenesis and therapy, aiming to provide valuable insights into the potential of targeting MTF pathways for the reseach of therapeutic strategies.

Tobacco-induced hyperglycemia promotes lung cancer progression via cancer cell-macrophage interaction through paracrine IGF2/IR/NPM1-driven PD-L1 expression

Tobacco smoking (TS) is implicated in lung cancer (LC) progression through the development of metabolic syndrome. However, direct evidence linking metabolic syndrome to TS-mediated LC progression remains to be established. Our findings demonstrate that 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and benzo[a]pyrene (NNK and BaP; NB), components of tobacco smoke, induce metabolic syndrome characteristics, particularly hyperglycemia, promoting lung cancer progression in male C57BL/6 J mice. NB enhances glucose uptake in tumor-associated macrophages by increasing the expression and surface localization of glucose transporter (GLUT) 1 and 3, thereby leading to transcriptional upregulation of insulin-like growth factor 2 (IGF2), which subsequently activates insulin receptor (IR) in LC cells in a paracrine manner, promoting its nuclear import. Nuclear IR binds to nucleophosmin (NPM1), resulting in IR/NPM1-mediated activation of the CD274 promoter and expression of programmed death ligand-1 (PD-L1). Restricting glycolysis, depleting macrophages, or blocking PD-L1 inhibits NB-mediated LC progression. Analysis of patient tissues and public databases reveals elevated levels of IGF2 and GLUT1 in tumor-associated macrophages, as well as tumoral PD-L1 and phosphorylated insulin-like growth factor 1 receptor/insulin receptor (pIGF-1R/IR) expression, suggesting potential poor prognostic biomarkers for LC patients. Our data indicate that paracrine IGF2/IR/NPM1/PD-L1 signaling, facilitated by NB-induced dysregulation of glucose levels and metabolic reprogramming of macrophages, contributes to TS-mediated LC progression.

Caveolae Microdomains Mediate STAT5 Signaling Induced by Insulin in MCF-7 Breast Cancer Cells

Caveolae are small plasma membrane invaginations constituted for membrane proteins namely caveolins and cytosolic proteins termed cavins, which can occupy up to 50% of the surface of mammalian cells. The caveolae have been involved with a variety of cellular processes including regulation of cellular signaling. Insulin is a hormone that mediates a variety of physiological processes through activation of insulin receptor (IR), which is a tyrosine kinase receptor expressed in all mammalian tissues. Insulin induces activation of signal transducers and activators of transcription (STAT) family members including STAT5. In this study, we demonstrate, for the first time, that insulin induces phosphorylation of STAT5 at tyrosine-694 (STAT5-Tyr(P)⁶⁹⁴), STAT5 nuclear accumulation and an increase in STAT5-DNA complex formation in MCF-7 breast cancer cells. Insulin also induces nuclear accumulation of STAT5-Tyr(P)⁶⁹⁴, caveolin-1, and IR in MCF-7 cells. STAT5 nuclear accumulation and the increase of STAT5-DNA complex formation require the integrity of caveolae and microtubule network. Moreover, insulin induces an increase and nuclear accumulation of STAT5-Tyr(P)⁶⁹⁴ in MDA-MB-231 breast cancer cells. In conclusion, results demonstrate that caveolae and microtubule network play an important role in STAT5-Tyr(P)⁶⁹⁴, STAT5 nuclear accumulation and STAT5-DNA complex formation induced by insulin in breast cancer cells.

Shuttling of cellular proteins between the plasma membrane and nucleus (Review)

Recently accumulated evidence has indicated that the nucleomembrane shuttling of cellular proteins is common, which provides new insight into the subcellular translocation and biological functions of proteins synthesized in the cytoplasm. The present study aimed to clarify the trafficking of proteins between the plasma membrane and nucleus. These proteins primarily consist of transmembrane receptors, membrane adaptor proteins, adhesive proteins, signal proteins and nuclear proteins, which contribute to proliferation, apoptosis, chemoresistance, adhesion, migration and gene expression. The proteins frequently undergo cross-talk, such as the interaction of transmembrane proteins with signal proteins. The transmembrane proteins undergo endocytosis, infusion into organelles or proteolysis into soluble forms for import into the nucleus, while nuclear proteins interact with membrane proteins or act as receptors. The nucleocytosolic translocation involves export or import through nuclear membrane pores by importin or exportin. Nuclear proteins generally interact with other transcription factors, and then binding to the promoter for gene expression, while membrane proteins are responsible for signal initiation by binding to other membrane and/or adaptor proteins. Protein translocation occurs in a cell-specific manner and is closely linked to cellular biological events. The present review aimed to improve understanding of cytosolic protein shuttling between the plasma membrane and nucleus and the associated signaling pathways.

Insulin-mediated immune dysfunction in the development of preeclampsia

Epidemiological observations implicate insulin resistance as a predisposing factor in the development of preeclampsia (PE). It is also well established that PE manifests in the context of a dysregulated immune response at the maternal-foetal interface, though all the underlying drivers of such immune dysregulation remains to be accounted for. Although it has long been known that various immune cells express insulin receptors following immune activation, it is only recently that insulin signalling has been shown to play a key role in immune cell differentiation, survival and effector function through its canonical activation of the PI3K/Akt/mTOR pathway. Here we argue that hyperinsulinemia, manifesting either from insulin resistance or from intensive insulin therapy, likely plays a direct role in driving immune cell dysfunction which plays a central role in the development of PE. This line of reasoning also explains the superior results of insulin-sparing interventions compared to intensive insulin therapy as monotherapy.

Exercise as a drug for glucose management and prevention in type 2 diabetes mellitus

Physical inactivity and sedentary behavior are risk factors for type 2 diabetes mellitus (T2DM). Therefore, physical exercise (PE) together with medical treatment might be considered as a key strategy to counteract T2DM. Glycemic control is a central objective in the prevention and management of T2DM, and PE might be able to substantially affect the processes that determine it. Just like a drug, exercise can be dosed based on the characteristics of the individual to increase its benefits and reduce side effects. In this brief review, the mechanisms underlying the effects of PE on glucose metabolism in muscle are illustrated, and the effects of modulation of the parameters characterizing this atypical "drug" on glucose homeostasis are described.

Gastrin, via activation of PPARα, protects the kidney against hypertensive injury

Hypertensive nephropathy (HN) is a common cause of end-stage renal disease with renal fibrosis; chronic kidney disease is associated with elevated serum gastrin. However, the relationship between gastrin and renal fibrosis in HN is still unknown. We, now, report that mice with angiotensin II (Ang II)-induced HN had increased renal cholecystokinin receptor B (CCKBR) expression. Knockout of CCKBR in mice aggravated, while long-term subcutaneous infusion of gastrin ameliorated the renal injury and interstitial fibrosis in HN and unilateral ureteral obstruction (UUO). The protective effects of gastrin on renal fibrosis can be independent of its regulation of blood pressure, because in UUO, gastrin decreased renal fibrosis without affecting blood pressure. Gastrin treatment decreased Ang II-induced renal tubule cell apoptosis, reversed Ang II-mediated inhibition of macrophage efferocytosis, and reduced renal inflammation. A screening of the regulatory factors of efferocytosis showed involvement of peroxisome proliferator-activated receptor α (PPAR-α). Knockdown of PPAR-α by shRNA blocked the anti-fibrotic effect of gastrin in vitro in mouse renal proximal tubule cells and macrophages. Immunofluorescence microscopy, Western blotting, luciferase reporter, and Cut&tag-qPCR analyses showed that CCKBR may be a transcription factor of PPAR-α, because gastrin treatment induced CCKBR translocation from cytosol to nucleus, binding to the PPAR-α promoter region, and increasing PPAR-α gene transcription. In conclusion, gastrin protects against HN by normalizing blood pressure, decreasing renal tubule cell apoptosis, and increasing macrophage efferocytosis. Gastrin-mediated CCKBR nuclear translocation may make it act as a transcription factor of PPAR-α, which is a novel signaling pathway. Gastrin may be a new potential drug for HN therapy.

Cell differentiation and aging accompanied by depletion of the ACE2 protein

ACE2 was observed as the cell surface receptor of the SARS-CoV-2 virus. Interestingly, we also found ACE2 positivity inside the cell nucleus. The ACE2 levels changed during cell differentiation and aging and varied in distinct cell types. We observed ACE2 depletion in the aortas of aging female mice, similarly, the aging caused ACE2 decrease in the kidneys. Compared with that in the heart, brain and kidneys, the ACE2 level was the lowest in the mouse lungs. In mice exposed to nicotine, ACE2 was not changed in olfactory bulbs but in the lungs, ACE2 was upregulated in females and downregulated in males. These observations indicate the distinct gender-dependent properties of ACE2.

Differentiation into enterocytes, and cardiomyocytes, caused ACE2 depletion. The cardiomyogenesis was accompanied by renin upregulation, delayed in HDAC1-depleted cells. In contrast, vitamin D2 decreased the renin level while ACE2 was upregulated. Together, the ACE2 level is high in non-differentiated cells. This protein is more abundant in the tissues of mouse embryos and young mice in comparison with older animals. Mostly, downregulation of ACE2 is accompanied by renin upregulation. Thus, the pathophysiology of COVID-19 disease should be further studied not only by considering the ACE2 level but also the whole renin-angiotensin system.

Nuclear receptor tyrosine kinase transport and functions in cancer

Signaling functions of plasma membrane-localized receptor tyrosine kinases (RTKs) have been extensively studied after they were first described in the mid-1980s. Plasma membrane RTKs are activated by extracellular ligands and cellular stress stimuli, and regulate cellular responses by activating the downstream effector proteins to initiate a wide range of signaling cascades in the cells. However, increasing evidence indicates that RTKs can also be transported into the intracellular compartments where they phosphorylate traditional effector proteins and non-canonical substrate proteins. In general, internalization that retains the RTK's transmembrane domain begins with endocytosis, and endosomal RTK remains active before being recycled or degraded. Further RTK retrograde transport from endosome-Golgi-ER to the nucleus is primarily dependent on membranes vesicles and relies on the interaction with the COP-I vesicle complex, Sec61 translocon complex, and importin. Internalized RTKs have non-canonical substrates that include transcriptional co-factors and DNA damage response proteins, and many nuclear RTKs harbor oncogenic properties and can enhance cancer progression. Indeed, nuclear-localized RTKs have been shown to positively correlate with cancer recurrence, therapeutic resistance, and poor prognosis of cancer patients. Therefore, understanding the functions of nuclear RTKs and the mechanisms of nuclear RTK transport will further improve our knowledge to evaluate the potential of targeting nuclear RTKs or the proteins involved in their transport as new cancer therapeutic strategies.

Insulin Receptor Trafficking: Consequences for Insulin Sensitivity and Diabetes

Insulin receptor (INSR) has been extensively studied in the area of cell proliferation and energy metabolism. Impaired INSR activities lead to insulin resistance, the key factor in the pathology of metabolic disorders including type 2 diabetes mellitus (T2DM). The mainstream opinion is that insulin resistance begins at a post-receptor level. The role of INSR activities and trafficking in insulin resistance pathogenesis has been largely ignored. Ligand-activated INSR is internalized and trafficked to early endosome (EE), where INSR is dephosphorylated and sorted. INSR can be subsequently conducted to lysosome for degradation or recycled back to the plasma membrane. The metabolic fate of INSR in cellular events implies the profound influence of INSR on insulin signaling pathways. Disruption of INSR-coupled activities has been identified in a wide range of insulin resistance-related diseases such as T2DM. Accumulating evidence suggests that alterations in INSR trafficking may lead to severe insulin resistance. However, there is very little understanding of how altered INSR activities undermine complex signaling pathways to the development of insulin resistance and T2DM. Here, we focus this review on summarizing previous findings on the molecular pathways of INSR trafficking in normal and diseased states. Through this review, we provide insights into the mechanistic role of INSR intracellular processes and activities in the development of insulin resistance and diabetes.

RIP at the Synapse and the Role of Intracellular Domains in Neurons

Regulated intramembrane proteolysis (RIP) occurs in a cell when transmembrane proteins are cleaved by intramembrane proteases such as secretases to generate soluble protein fragments in the extracellular environment and the cytosol. In the cytosol, these soluble intracellular domains (ICDs) have local functions near the site of cleavage or in many cases, translocate to the nucleus to modulate gene expression. While the mechanism of RIP is relatively well studied, the fate and function of ICDs for most substrate proteins remain poorly characterized. In neurons, RIP occurs in various subcellular compartments including at the synapse. In this review, we summarize current research on RIP in neurons, focusing specifically on synaptic proteins where the presence and function of the ICDs have been reported. We also briefly discuss activity-driven processing of RIP substrates at the synapse and the cellular machinery that support long-distance transport of ICDs from the synapse to the nucleus. Finally, we describe future challenges in this field of research in the context of understanding the contribution of ICDs in neuronal function.