Overexpression of membrane glycoprotein PC-1 in MDA-MB231 breast cancer cells is associated with inhibition of insulin receptor tyrosine kinase activity

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

Endocrine role of bone: recent and emerging perspectives beyond osteocalcin

Recent developments in endocrinology, made possible by the combination of mouse genetics, integrative physiology and clinical observations have resulted in rapid and unanticipated advances in the field of skeletal biology. Indeed, the skeleton, classically viewed as a structural scaffold necessary for mobility, and regulator of calcium-phosphorus homoeostasis and maintenance of the haematopoietic niche has now been identified as an important regulator of male fertility and whole-body glucose metabolism, in addition to the classical insulin target tissues. These seminal findings confirm bone to be a true endocrine organ. This review is intended to detail the key events commencing from the elucidation of osteocalcin (OC) in bone metabolism to identification of new and emerging candidates that may regulate energy metabolism independently of OC.

The cellular and molecular mechanisms by which insulin influences breast cancer risk and progression

Epidemiological studies have related hyperinsulinemia and type 2 diabetes to an increased breast cancer risk, an aggressive and metastatic phenotype, and a poor prognosis. Furthermore, diabetic retinopathy arises from pathological angiogenesis, which is also essential for breast cancer growth and metastasis. Insulin stimulates the proliferation of some human breast cancer cell lines in vitro by mechanisms that use both the phosphatidylinositol-3 kinase and the mitogen-activated protein kinase/Akt signaling pathways; it is also a cell survival (anti-apoptotic) agent and enhances tumor cell migration and invasive capacity. Hyperinsulinemia affects breast cancer cells via the endocrine system, but experimental studies suggest the importance of paracrine mechanisms operating by the effects of insulin on the secretion of adipokines from tumor-associated adipose tissue. In such a system, one adipokine, leptin, has stimulatory paracrine effects on breast cancer cell proliferation and survival, while a second, adiponectin, is inhibitory. Leptin, vascular endothelial growth factor, another insulin-regulated adipokine, and insulin itself also stimulate angiogenesis. Insulin has complex interactions with estrogens: it induces adipose stromal cell aromatase and tumor cell sex steroid hormone receptor expression and suppresses sex hormone-binding globulin, which may enhance estrogen synthesis and bioactivity with consequent promotion of estrogen-dependent breast cancer. All these actions influence the later steps in breast cancer development but genetic studies are also revealing connections between gene abnormalities related to type 2 diabetes and the initiation stage of breast carcinogenesis. Understanding the various mechanisms by which insulin participates in breast cancer cell biology provides opportunities for novel approaches to treatment.

Insulin receptor and cancer

The widespread epidemic of obesity and type 2 diabetes has raised concern for the impact of these disorders as risk factors for cancer and has renewed the interest for studies regarding the involvement of hyperinsulinemia and insulin receptor (IR) in cancer progression. Overexpression of IR in cancer cells may explain their increased sensitivity to hyperinsulinemia. Moreover, IR isoform A (IR-A) together with autocrine production of its ligand IGF2 is emerging as an important mechanism of normal and cancer stem cell expansion and is a feature of several malignancies. De novo activation of the IR-A/IGF2 autocrine loop also represents a mechanism of resistance to anticancer therapies. Increasing knowledge of the IR role in cancer has important implications for cancer prevention, which should include control of insulin resistance and hyperinsulinemia in the population and meticulous evaluation of new antidiabetic drugs for their metabolic:mitogenic ratio. We are now aware that several anticancer treatments may induce or worsen insulin resistance that may limit therapy efficacy. Future anticancer therapies need to target the IR-A pathway in order to inhibit the tumor promoting effect of IR without impairing the metabolic effect of insulin.

The CNK1 scaffold binds cytohesins and promotes insulin pathway signaling

Protein scaffolds play an important role in signal transduction, regulating the localization of signaling components and mediating key protein interactions. Here, we report that the major binding partners of the Connector Enhancer of KSR 1 (CNK1) scaffold are members of the cytohesin family of Arf guanine nucleotide exchange factors, and that the CNK1/cytohesin interaction is critical for activation of the PI3K/AKT cascade downstream from insulin and insulin-like growth factor 1 (IGF-1) receptors. We identified a domain located in the C-terminal region of CNK1 that interacts constitutively with the coiled-coil domain of the cytohesins, and found that CNK1 facilitates the membrane recruitment of cytohesin-2 following insulin stimulation. Moreover, through protein depletion and rescue experiments, we found that the CNK1/cytohesin interaction promotes signaling from plasma membrane-bound Arf GTPases to the phosphatidylinositol 4-phosphate 5-kinases (PIP5Ks) to generate a PIP(2)-rich microenvironment that is critical for the membrane recruitment of insulin receptor substrate 1 (IRS1) and signal transmission to the PI3K/AKT cascade. These findings identify CNK1 as a new positive regulator of insulin signaling.

Evidence that inhibition of insulin receptor signaling activity by PC-1/ENPP1 is dependent on its enzyme activity

Plasma cell membrane glycoprotein-1 or ectonucleotide pyrophosphatase/phosphodiesterase (PC-1/ENPP1) has been shown to inhibit insulin signaling, and its genetic polymorphism or increased expression is associated with type 2 diabetes in humans. Therefore, PC-1 inhibition represents a potential strategy in treating diabetes. Since patients with phosphodiesterase/pyrophosphatase deficient PC-1 manifest abnormal calcification, enhancing insulin signaling by inhibiting PC-1 for the treatment of diabetes will be feasible only if PC-1 phosphodiesterase/pyrophosphatase activity needs not be significantly diminished. However, whether inhibition of insulin receptor signaling by PC-1 is dependent upon its phosphodiesterase/pyrophosphatase activity remains controversial. In this study, the extracellular domain of the human PC-1 in its native form or with a T256A or T256S mutation was overexpressed and purified. Enzymatic assays showed that both mutants have less than 10% of the activity of the wild-type protein. In HEK293 cells stably expressing recombinant insulin receptor or insulin-like growth factor 1 (IGF1) receptor, transient expression of wild-type full length PC-1 (PC-1.FL.WT) but not the T256A or T256S mutants inhibits insulin signaling without affecting IGF1 signaling. Western blot and FACS analysis showed that the wild-type and mutant full length PC-1 proteins are expressed at similar levels in the cells, and were localized to the similar levels on the cell surface. Overexpression of PC-1.FL.WT did not affect insulin receptor mRNA level, total protein and cell surface levels. Together, these results suggest that the inhibition of insulin signaling by PC-1 is somewhat specific and is dependent upon the enzymatic activity of the phosphodiesterase/pyrophosphatase.

Increased activity of membrane glycoprotein PC-1 in the fibroblasts from non-insulin-dependent diabetes mellitus patients with insulin resistance

Although most of patients with non-insulin-dependent diabetes mellitus (NIDDM) have insulin resistance, it is unknown whether a molecule might interfere with insulin action. Membrane glycoprotein PC-1 (plasma cell antigen-1), which inhibits insulin receptor tyrosine kinase activity, was isolated from fibroblasts of NIDDM patients. Because PC-1 content in skeletal muscle and adipose tissue correlated with whole body insulin sensitivity, PC-1 might play a role in insulin resistance. In order to know whether PC-1 activity of fibroblasts is also elevated in Japanese NIDDM patients, and whether PC-1 activity correlates with the parameters of insulin resistance in vivo or not, we measured PC-1 activity of cultured fibroblasts from 17 patients with NIDDM and seven healthy controls. PC-1 activity of the NIDDM patients was 85.2 +/- 33.1 nmol/mg per min (mean +/- S.D.), and was higher than that of healthy controls (42.6 +/- 12.7 nmol/mg per min, P = 0.0002). Insulin sensitivity was measured in 11 of 17 NIDDM patients by the artificial pancreas. PC-1 activity of the patients with insulin resistance (glucose infusion rate < 3.0 mg/kg per min, n = 7) was elevated to 99.9 +/- 31.9 nmol/mg per min, while that of the other patients (n = 4) was 55.3 +/- 7.5 nmol/mg per min (P = 0.003). In conclusion, glycoprotein PC-1 activity of dermal fibroblasts is correlated with insulin resistance in patients with NIDDM.

Expression of the insulin-like growth factor 1 receptor (IGF-1R) in breast cancer cells: evidence for a regulatory role of dolichyl phosphate in the transition from an intracellular to an extracellular IGF-1 pathway

In this study we provide evidence that the low expression of IGF-1R at the cell surface of estrogen-independent breast cancer cells is due to a low rate of de novo synthesis of dolichyl phosphate. The analyses were performed on the estrogen receptor-negative breast cancer cell line MDA231 and, in comparison, the melanoma cell line SK-MEL-2, which expresses a high number of plasma membrane-bound IGF-1R. Whereas the MDA231 cells had little or no surface expression of IGF-1R, they expressed functional (i.e., ligand-binding) intracellular receptors. By measuring the incorporation of [3H]mevalonate into dolichyl phosphate, we could demonstrate that the rate of dolichyl phosphate synthesis was considerably lower in MDA231 cells than in SK-MEL-2 cells. Furthermore, N-linked glycosylation of the alpha-subunit of IGF-1R was 8-fold higher in the melanoma cells. Following addition of dolichyl phosphate to MDA231 cells, N-linked glycosylation of IGF-1R was drastically increased, which in turn was correlated to a substantial translocation of IGF-1R to the plasma membrane, as assayed by IGF-1 binding analysis and by Western blotting of plasma membrane proteins. The dolichyl phosphate-stimulated receptors were proven to be biochemically active since they exhibited autophosphorylation. Under normal conditions MDA231 cells, expressing very few IGF-1R at the cell surface, were not growth-arrested by an antibody (alphaIR-3) blocking the binding of IGF-1 to IGF-1R. However, after treatment with dolichyl phosphate, leading to a high cell surface expression of IGF-1R, alphaIR-3 efficiently blocked MDA231 cell growth. Taken together with the fact that the breast cancer cells produce IGF-1 and exhibit intracellular binding, our data suggest that the level of de novo -synthesized dolichyl phosphate may be critical for whether the cells will use an intracellular or an extracellular autocrine IGF-1 pathway.

The insulin receptor--a critical link in glucose homeostasis and insulin action

We have achieved significant progress in understanding the central role of the insulin receptor in an increasingly complicated web of intracellular signal transduction leading to the ultimate biological actions of insulin on glucose, lipid, and other metabolic pathways. The excitement for the future lies not only in clarifying these pathways but also returning to whole-body physiology to readdress basic mechanisms of insulin action in known and novel insulin-sensitive tissues. Hopefully, these new techniques and new perspectives will bring us closer to understanding the pathophysiology of type 2 diabetes mellitus.

Ecto-phosphodiesterase/pyrophosphatase of lymphocytes and non-lymphoid cells: structure and function of the PC-1 family

Many developmentally regulated membrane proteins of lymphocytes are ecto-enzymes, with their active sites on the external surface of the cell. These enzymes commonly have peptidase, phosphodiesterase or nucleotidase activity. Their biological roles are just beginning to be discovered. Although their expression is usually associated with particular stages of lymphoid differentiation, the same gene products are often expressed on the surface of certain non-lymphoid cell types outside the immune system, indicating that their functions cannot be unique to lymphocytes, nor can they be ubiquitous. The plasma cell membrane protein PC-1 (phosphodiesterase I; EC 3.1.4.1/nucleotide pyrophosphatase; EC 3.6.1.9), which was one of the first serological markers for lymphocyte subsets to be discovered, is a typical example. Within the immune system, PC-1 is confined to plasma cells, which represent about 0.1% of lymphocytes. However, PC-1 is also expressed on cells of the distal convoluted tubule of the kidney, chondrocytes, osteoblasts, epididymis and hepatocytes. Recent work has shown that PC-1 is a member of a multigene family of ecto-phosphodiesterases that currently has two other members, PD-1 alpha (autotaxin) and PD-1 beta (B10). Within this family, the extracellular domains are highly conserved, especially around the active site. In contrast, the transmembrane and cytoplasmic domains are highly divergent. Individual members of the eco-phosphodiesterase family have distinct patterns of distribution in different cell types, and even within the same cell. For example, PC-1 is present only on the basolateral surface of hepatocytes, while B10 (PD-1 beta) is confined to the apical surface. Analysis of conservation and differences in the sequence of their cytoplasmic tails may illuminate intracellular targetting signals. Ecto-phosphodiesterases may play a part in diverse activities in different tissues, including recycling of nucleotides. They may also regulate the concentration of pharmacologically active extracellular compounds such as adenosine or its derivatives and cell motility. Some members may modulate local concentrations of pyrophosphate, and hence influence calcification in bone and cartilage.

Insulin receptor what role in breast cancer?

It is commonly believed that the insulin receptor mainly mediates the metabolic effects of insulin, whereas the closely related IGF-I receptor is considered a major factor for the regulation of cell proliferation. Experimental and epidemiological evidence indicates, however, that insulin and insulin receptors may play an important role in breast cancer. This article reviews evidence indicating that (a) insulin receptors are overexpressed in human breast cancer, (b) insulin stimulates growth in breast cancer cells, (c) cells transfected with human insulin receptor may acquire a ligand-dependent transformed phenotype, and (d) breast cancer is associated with insulin resistance and hyperinsulinemia. These findings may open new possibilities in breast cancer prevention, prognosis assessment, and therapy. (Trends Endocrinol Metab 1997; 8:306-312). (c) 1997, Elsevier Science Inc.