A Noncanonical Role of Fructose-1, 6-Bisphosphatase 1 Is Essential for Inhibition of Notch1 in Breast Cancer

Fructose-1,6-bisphosphatase 1 in cancer: Dual roles, mechanistic insights, and therapeutic potential - A comprehensive review

Fructose-1,6-bisphosphatase 1 (FBP1) is a key gluconeogenic enzyme that plays complex and context-dependent roles in cancer biology. This review comprehensively examines FBP1's dual functions as both a tumor suppressor and an oncogene across various cancer types. In many cancers, such as hepatocellular carcinoma, clear cell renal cell carcinoma, and lung cancer, downregulation of FBP1 contributes to tumor progression through metabolic reprogramming, promoting glycolysis, and altering the tumor microenvironment. Conversely, in certain contexts like breast and prostate cancers, FBP1 overexpression is associated with tumor promotion, indicating its oncogenic potential. The review explores FBP1's interactions with immune cells within the tumor microenvironment, influencing immune surveillance and tumor immune escape mechanisms. Additionally, FBP1 emerges as a promising diagnostic and prognostic biomarker, with expression levels correlating with patient outcomes in multiple cancers. Future therapeutic strategies targeting FBP1 are discussed, including inhibitors, activators, epigenetic modulation, and combination therapies, while addressing the challenges posed by its dual nature. Understanding the multifaceted roles of FBP1 offers valuable insights into cancer metabolism and opens avenues for personalized therapeutic interventions.

PAK5-mediated PKM2 phosphorylation is critical for anaerobic glycolysis in endometriosis

P21-activated kinase 5 (PAK5) belongs to the PAK-II subfamily, which is an important regulator of cell survival, adhesion, and motility. However, the functions of PAK5 in endometriosis remain unclear. Here, PAK5 is strikingly upregulated in endometriosis. Furthermore, the knockdown of PAK5 or its inhibitor GNE 2861 blocks the development of endometriosis, which is equally demonstrated in PAK5-knockout mice. In addition, PAK5 promotes glycolysis by enhancing the protein stability of pyruvate kinase 2 (PKM2) in endometriotic cells, which is a key enzyme for glucose metabolism. Moreover, the phosphorylation of PKM2 at Ser519 by PAK5 mediates endometriosis cell proliferation and metastasis. Collectively, PAK5 plays an indispensable role in endometriosis. Our findings demonstrate that PAK5 is an important target for the treatment of endometriosis.

CADM2 participates in endometriosis development by influencing the epithelial-mesenchymal transition

Endometriosis (EM) is a common gynecologic condition that often leads to infertility in women of reproductive age. Cell adhesion molecule 2 (CADM2) is involved in maintaining cell adhesion and polarity, as well as suppressing tumors. However, the role and mechanism of CADM2 in endometriosis is unclear. Therefore, this study evaluated the expression levels of CADM2 and epithelial-mesenchymal transition (EMT)-related marker proteins (E-cadherin, α-SMA, and N-cadherin). Compared to normal endometrial tissue, CADM2 was expressed at low levels in ectopic endometrial tissue from patients with EM. We performed clone formation assays, wound healing assays, and Transwell cell invasion assays to investigate the effects of CADM2 on the biological behavior of endometriosis epithelial cells (11Z) and ectopic endometrial stromal cells (EESCs). The growth, migration, and invasion abilities of these cells were significantly inhibited by overexpression of CADM2. The results were reversed after the knockdown of CADM2. Finally, western blotting (WB) was utilized to detect the effect of CADM2 on EMT in endometriosis cells. CADM2 inhibited EMT in endometriosis cells. In conclusion, our study suggests that CADM2 is a negative regulator of endometriosis development and may inhibit endometriosis development by suppressing EMT.

Phosphorylation of USP27X by PIM2 promotes glycolysis and breast cancer progression via deubiquitylation of MYC

Aberrant cell proliferation is a hallmark of cancer, including breast cancer. Here, we show that USP27X is required for cell proliferation and tumorigenesis in breast cancer. We identify a PIM2-USP27X regulator of MYC signaling axis whose activity is an important contributor to the tumor biology of breast cancer. PIM2 phosphorylates USP27X, and promotes its deubiquitylation activity for MYC, which promotes its protein stability and leads to increase HK2-mediated aerobic glycolysis in breast cancer. Moreover, the PIM2-USP27X-MYC axis is also validated in PIM2-knockout mice. Taken together, these findings show a PIM2-USP27X-MYC signaling axis as a new potential target for breast cancer treatment.

FBP1 inhibits NSCLC stemness by promoting ubiquitination of Notch1 intracellular domain and accelerating degradation

The existence of cancer stem cells is widely acknowledged as the underlying cause for the challenging curability and high relapse rates observed in various tumor types, including non-small cell lung cancer (NSCLC). Despite extensive research on numerous therapeutic targets for NSCLC treatment, the strategies to effectively combat NSCLC stemness and achieve a definitive cure are still not well defined. The primary objective of this study was to examine the underlying mechanism through which Fructose-1,6-bisphosphatase 1 (FBP1), a gluconeogenic enzyme, functions as a tumor suppressor to regulate the stemness of NSCLC. Herein, we showed that overexpression of FBP1 led to a decrease in the proportion of CD133-positive cells, weakened tumorigenicity, and decreased expression of stemness factors. FBP1 inhibited the activation of Notch signaling, while it had no impact on the transcription level of Notch 1 intracellular domain (NICD1). Instead, FBP1 interacted with NICD1 and the E3 ubiquitin ligase FBXW7 to facilitate the degradation of NICD1 through the ubiquitin-proteasome pathway, which is independent of the metabolic enzymatic activity of FBP1. The aforementioned studies suggest that targeting the FBP1-FBXW7-NICD1 axis holds promise as a therapeutic approach for addressing the challenges of NSCLC recurrence and drug resistance.

PFKFB3 promotes endometriosis cell proliferation via enhancing the protein stability of β-catenin

Endometriosis is a common inflammatory disease in women of reproductive age and is highly associated with infertility. However, the molecular mechanism of endometriosis remains unclear. 6-Phosphofructose-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) is a key enzyme in glycolysis and plays an important regulatory role in the development of cancer. Here we found that PFKFB3 is highly expressed in endometriotic tissues. PFKFB3 promotes the proliferation and growth of endometriosis cells. Meanwhile, PFKFB3 promotes glycolysis in endometriosis cells. Furthermore, PFKFB3 promotes migration and invasion of endometriosis cells. On this basis, we found that PFKFB3 promotes epithelial-mesenchymal transition (EMT) in endometriosis cells. PFKFB3 interacts with the essential factor of EMT, β-catenin, and promotes the protein stability of β-catenin. In addition, the PFKFB3 inhibitor PFK-015 inhibites the growth of endometriosis cells and the development of endometrial tissue. In conclusion, our study shows that PFKFB3 plays an important role in the development of endometriosis and provides new ideas for the clinical diagnosis or treatment of endometriosis.

FDX1 enhances endometriosis cell cuproptosis via G6PD-mediated redox homeostasis

Cuproptosis is a new form of programmed cell death, which is associated with the mitochondrial TCA (tricarboxylic acid) cycle. But the functions of cuproptosis in endometriosis progression are still unknown. Here, we find that cuproptosis suppresses the growth of endometriosis cells and the growth of ectopic endometrial tissues in a mouse model. FDX1 as a key regulator in cuproptosis pathway could promote cuproptosis in endometriosis cells. Interestingly, FDX1 interacts with G6PD, and reduces its protein stability, which predominantly affects the cellular redox-regulating systems. Then, the reduced G6PD activity enhances cuproptosis via down-regulating NADPH and GSH levels. Collectively, our study demonstrates that FDX1 mediates cuproptosis in endometriosis via G6PD pathway, resulting in repression of endometriosis cell proliferation and metastasis.

CHIP induces ubiquitination and degradation of HMGB1 to regulate glycolysis in ovarian endometriosis

Ovarian endometriosis is a common gynecological condition that can cause infertility in women of childbearing age. However, the pathogenesis is still unknown. We demonstrate that the carboxyl terminus of Hsc70-interacting protein (CHIP) is a negative regulator in the development of endometriosis and reduces HMGB1 expression in endometriotic cells. Meanwhile, CHIP interacts with HMGB1 and promotes its ubiquitinated degradation, thereby inhibiting aerobic glycolysis and the progression of endometriosis. Furthermore, the CHIP agonist YL-109 effectively suppresses the growth of ectopic endometrium in endometriosis mouse model, which could be a potential therapeutic approach for endometriosis. In conclusion, our data suggest that CHIP may inhibit the development of endometriosis by suppressing the HMGB1-related glycolysis.

Phosphorylation of PFKFB4 by PIM2 promotes anaerobic glycolysis and cell proliferation in endometriosis

Endometriosis (EM) is one of the vanquished wonted causes of chronic pelvic sting in women and is closely associated with infertility. The long-term, complex, systemic, and post-treatment recurrence of EM wreaks havoc on women's quality of life. Extensive metabolic reprogramming (aerobic glycolysis, glucose overweening intake, and high lactate production) and cancer-like changes have been found in EM, which bears striking similarities to tumorigenesis. The key glycolysis regulator PFKFB4 is overexpressed in EM. However, the mechanism of PFKFB4 in EM remains unknown. We found that PFKFB4 was upregulated and was closely related to the progression of EM. We identified focus PIM2 as a new pioneering adjoin protein of PFKFB4. Vigorous biochemical methods were used to confirm that PIM2 phosphorylated site Thr140 of PFKFB4. PIM2 also could enhance PFKFB4 protein expression through the ubiquitin-proteasome pathway. Moreover, PIM2 expression was really corresponding prevalent with PFKFB4 in endometriosis in vivo. Importantly, phosphorylation of PFKFB4 on Thr140 by PIM2 promoted EM glycolysis and cell growth. Our study demonstrates that PIM2 mediates PFKFB4 Thr140 phosphorylation thus regulating glycolysis and EM progression. We illustrated a new mechanism that PIM2 simulated a central upstream partnership in the regulation of PFKFB4, and reveal a novel means of PIM2-PFKFB4 setting EM growth. Our research provided new theoretical support for further clarifying the reprogramming of EM glucose metabolism, and provided new clues for exploring non-contraceptive treatments for EM.

SMYD3 promotes aerobic glycolysis in diffuse large B-cell lymphoma via H3K4me3-mediated PKM2 transcription

Genetic abnormalities in histone methyltransferases (HMTs) frequently occur in diffuse large B-cell lymphoma (DLBCL) and are related to its progression. SET and MYND domain containing 3 (SMYD3) is an HMT that is upregulated in various tumors and promotes their malignancy. However, to the best of our knowledge, the function of SMYD3 in DLBCL has not been investigated thus far. In the present study, 22 HMT genes related to cancer development were first selected according to current literature, and it was found that high SMYD3 expression was significantly associated with poor progression-free survival in patients with DLBCL. SMYD3 protein levels were upregulated and positively associated with poor prognosis and poor responsiveness to chemotherapy in patients with DLBCL. Functional examinations demonstrated that SMYD3 increased cell proliferation and the flux of aerobic glycolysis in DLBCL cells in vitro and in vivo and decreased cell sensitivity to doxorubicin in vitro. Moreover, SMYD3 could directly bind to specific sequences of Pyruvate Kinase M2 (PKM2) and promote DLBCL cell proliferation and aerobic glycolysis via H3K4me3-mediated PKM2 transcription. Clinically, SMYD3 expression positively correlated with that of PKM2, and high SMYD3 was significantly associated with high maximum standardized uptake value (SUVmax) detected by [(18)F]-fluorodeoxyglucose ((18)F-FDG) PET/computed tomography (PET/CT) in DLBCL samples. Concomitant expression of SMYD3 and PKM2 positively correlated with poor progression-free and overall survival in patients with DLBCL and may serve as novel biomarkers in DLBCL.

Glucagon signaling via supraphysiologic GCGR can reduce cell viability without stimulating gluconeogenic gene expression in liver cancer cells

Background

Deregulated glucose metabolism is a critical component of cancer growth and survival, clinically evident via FDG-PET imaging of enhanced glucose uptake in tumor nodules. Tumor cells utilize glucose in a variety of interconnected biochemical pathways to generate energy, anabolic precursors, and other metabolites necessary for growth. Glucagon-stimulated gluconeogenesis opposes glycolysis, potentially representing a pathway-specific strategy for targeting glucose metabolism in tumor cells. Here, we test the hypothesis of whether glucagon signaling can activate gluconeogenesis to reduce tumor proliferation in models of liver cancer.

Methods

The glucagon receptor, GCGR, was overexpressed in liver cancer cell lines consisting of a range of etiologies and genetic backgrounds. Glucagon signaling transduction was measured by cAMP ELISAs, western blots of phosphorylated PKA substrates, and qPCRs of relative mRNA expression of multiple gluconeogenic enzymes. Lastly, cell proliferation and apoptosis assays were performed to quantify the biological effect of glucagon/GCGR stimulation.

Results

Signaling analyses in SNU398 GCGR cells treated with glucagon revealed an increase in cAMP abundance and phosphorylation of downstream PKA substrates, including CREB. qPCR data indicated that none of the three major gluconeogenic genes, G6PC, FBP1, or PCK1, exhibit significantly higher mRNA levels in SNU398 GCGR cells when treated with glucagon; however, this could be partially increased with epigenetic inhibitors. In glucagon-treated SNU398 GCGR cells, flow cytometry analyses of apoptotic markers and growth assays reproducibly measured statistically significant reductions in cell viability. Finally, proliferation experiments employing siCREB inhibition showed no reversal of cell death in SNU398 GCGR cells treated with glucagon, indicating the effects of glucagon in this setting are independent of CREB.

Conclusions

For the first time, we report a potential tumor suppressive role for glucagon/GCGR in liver cancer. Specifically, we identified a novel cell line-specific phenotype, whereby glucagon signaling can induce apoptosis via an undetermined mechanism. Future studies should explore the potential effects of glucagon in diabetic liver cancer patients.

Ubiquitination of NF-κB p65 by FBXW2 suppresses breast cancer stemness, tumorigenesis, and paclitaxel resistance

The F-box and WD-repeat-containing protein 2 (FBXW2) plays a crucial role as an E3 ligase in regulating tumorigenesis. However, the functions of FBXW2 in breast cancer are still unknown. Here, we find that nuclear factor-kB (NF-κB) p65 is a new substrate of FBXW2. FBXW2 directly binds to p65, leading to its ubiquitination and degradation. Interestingly, p300 acetylation of p65 blocks FBXW2 induced p65 ubiquitination. FBXW2-p65 axis is a crucial regulator of SOX2-induced stemness in breast cancer. Moreover, FBXW2 inhibits breast tumor growth by regulating p65 degradation in vitro and in vivo. FBXW2 overexpression abrogates the effects of p65 on paclitaxel resistance in vitro and in vivo. Furthermore, FBXW2 induced p65 degradation is also confirmed in FBXW2-knockout mice. Our results identify FBXW2 as an important E3 ligase for p65 degradation, which provide insights into the tumor suppressor functions of FBXW2 in breast cancer.

Moonlighting functions of metabolic enzymes and metabolites in cancer

The growing field of tumor metabolism has greatly expanded our knowledge of metabolic reprogramming in cancer. Apart from their established roles, various metabolic enzymes and metabolites harbor non-canonical ("moonlighting") functions to support malignant transformation. In this article, we intend to review the current understanding of moonlighting functions of metabolic enzymes and related metabolites broadly existing in cancer cells by dissecting each major metabolic pathway and its regulation of cellular behaviors. Understanding these non-canonical functions may broaden the horizon of the cancer metabolism field and uncover novel therapeutic vulnerabilities in cancer.

HSF1 promotes endometriosis development and glycolysis by up-regulating PFKFB3 expression

BACKGROUND

Endometriosis is a chronic hormonal inflammatory disease characterized by the presence of endometrial tissue outside the uterus. Endometriosis often causes infertility, which brings physical and mental pain to patients and their families.

METHODS

We examined the functions of heat shock factor 1 (HSF1) in endometriosis development through cell count assay, cell-scratch assay and clone formation experiments. We used quantitative real-time PCR (qRT-PCR) and Western blot (WB) to detect HSF1 expression. Glucose and lactate levels were determined using a glucose (GO) assay kit and a lactate assay kit. Furthermore, we used a HSF1 inhibitor-KRIBB11 to establish a mouse model of endometriosis.

RESULTS

Our data demonstrated that HSF1 promoted endometriosis development. Interestingly, HSF1 enhanced glycolysis via up-regulating PFKFB3 expression in endometriosis cells, which was a key glycolysis enzyme. Consistently, the HSF1 inhibitor KRIBB11 could abrogate endometriosis progression in vivo and in vitro.

CONCLUSIONS

Findings indicate that HSF1 plays an important role in endometriosis development, which might become a new target for the treatment of endometriosis.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary data are available.

High expression of FBP1 and LDHB in fibroadenomas and invasive breast cancers

BACKGROUND

The role of gluconeogenesis in cancer cells as the reverse pathway for glycolysis is not well known. Several studies of gluconeogenesis in cancer cells still show conflicting results. Expression of key enzymes such as FBP1 and LDHB in cancer tissues may explain the role of gluconeogenesis in tumor development.

OBJECTIVE

This study aimed to analyze the expression of FBP1 and LDHB in fibroadenomas and invasive cancers of the breast.

METHODS

The immunohistochemical staining technique was used to show the expression of FBP1 and LDHB in formalin-fixed, paraffin-embedded blocks of 32 fibroadenomas and 31 invasive breast cancer samples.

RESULTS

FBP1 was expressed by the majority of fibroadenoma (68.7%) and invasive breast cancer (71%) samples. LDHB expression in fibroadenomas was significantly higher than in invasive breast cancers (P = 0.029). The expression of these two enzymes was found in lobular, ductal, and NST types of invasive breast cancers, and at low, intermediate, and high grades of malignancy.

CONCLUSIONS

High expression of FBP1 and LDHB was found in fibroadenomas and invasive breast cancers. A higher level of LDHB expression was observed in fibroadenomas. These results may indicate the enzymes' role in the pathogenesis of both breast diseases.

Fructose-1,6-bisphosphatase aggravates oxidative stress-induced apoptosis in asthma by suppressing the Nrf2 pathway

Asthma is a chronic airway disease that causes excessive inflammation, oxidative stress, mucus production and bronchial epithelial cell apoptosis. Fructose‐1,6‐bisphosphatase (Fbp1) is one of the rate‐limiting enzymes in gluconeogenesis and plays a critical role in several cancers. However, its role in inflammatory diseases, such as asthma, is unclear. Here, we examined the expression, function and mechanism of action of Fbp1 in asthma. Gene Expression Omnibus (GEO) data sets revealed that Fbp1 was overexpressed in a murine model of asthma and in interleukin (IL)‐4‐ or IL‐13‐stimulated bronchial epithelial cells. We confirmed the findings in an animal model as well as Beas‐2B and 16HBE cells. In vitro investigations revealed that silencing of Fbp1 reduced apoptosis and the proportion of cells in the G2/M phase, whereas overexpression led to increases. Fbp1 knock‐down inhibited oxidative stress by activating the nuclear factor erythroid 2‐related factor 2 (Nrf2) pathway, whereas Fbp1 overexpression aggravated oxidative stress by suppressingthe Nrf2 pathway. Moreover, the Nrf2 pathway inhibitor ML385 reversed the changes caused by Fbp1 inhibition in Beas‐2B and 16HBE cells. Collectively, our data indicate that Fbp1 aggravates oxidative stress‐induced apoptosis by suppressing Nrf2 signalling, substantiating its potential as a novel therapeutic target in asthma.

Proteins moonlighting in tumor metabolism and epigenetics

Cancer development is a complicated process controlled by the interplay of multiple signaling pathways and restrained by oxygen and nutrient accessibility in the tumor microenvironment. High plasticity in using diverse nutrients to adapt to metabolic stress is one of the hallmarks of cancer cells. To respond to nutrient stress and to meet the requirements for rapid cell proliferation, cancer cells reprogram metabolic pathways to take up more glucose and coordinate the production of energy and intermediates for biosynthesis. Such actions involve gene expression and activity regulation by the moonlighting function of oncoproteins and metabolic enzymes. The signal - moonlighting protein - metabolism axis facilitates the adaptation of tumor cells under varying environment conditions and can be therapeutically targeted for cancer treatment.

miR‑34c‑5p targets Notch1 and suppresses the metastasis and invasion of cervical cancer

Micro (mi)RNAs are crucial participants in the progression of cervical cancer (CC). Growing evidence indicates that miRNA (miR)-34c-5p is a pivotal tumor suppressor in numerous types of cancer and its functions in CC require further investigating. The present study demonstrated that there was a decreased level of miR-34c-5p in CC-associated cell lines compared with healthy control samples. It also demonstrated that miR-34c-5p targeted Notch1 and suppressed CC progression. Dual-Luciferase reporter assays verified the targeted relationship of miR-34c-5p and Notch1. The expression of Notch1 in HeLa cells was markedly reduced following miR-34c-5p overexpression and the proliferation, migration and invasion of HeLa cells were reduced although apoptosis was accelerated. However, overexpression of miR-34c-5p was reversed following the addition of Notch1, which supported the finding of the targeted relationship between miR-34c-5p and Notch1. Flow cytometry demonstrated that miR-34c-5p inhibited the proliferation of HeLa cells while accelerating apoptosis. The present study concluded that miR-34c-5p was a tumor suppressor in CC and may be a novel measure for the future treatment of CC.

Fructose-1, 6-bisphosphatase 1 interacts with NF-κB p65 to regulate breast tumorigenesis via PIM2 induced phosphorylation

Rationale: Fructose-1, 6-bisphosphatase 1 (FBP1), a rate-limiting enzyme in gluconeogenesis, was recently shown to be a tumor suppressor and could mediate the activities of multiple transcriptional factors via its non-canonical functions. However, the underlying mechanism of posttranscriptional modification on the non-canonical functions of FBP1 remains elusive.

Methods: We employed immunoaffinity purification to identify binding partner(s) and used co-immunoprecipitation to verify their interactions. Kinase reaction was used to confirm PIM2 could phosphorylate FBP1. Overexpression or knockdown proteins were used to assess the role in modulating p65 protein stability. Mechanistic analysis was involved in protein degradation and polyubiquitination assays. Nude mice and PIM2-knockout mice was used to study protein functions in vitro and in vivo.

Results: Here, we identified Proviral Insertion in Murine Lymphomas 2 (PIM2) as a new binding partner of FBP1, which could phosphorylate FBP1 on Ser144. Surprisingly, phosphorylated FBP1 Ser144 abrogated its interaction with NF-κB p65, promoting its protein stability through the CHIP-mediated proteasome pathway. Furthermore, phosphorylation of FBP1 on Ser144 increased p65 regulated PD-L1 expression. As a result, phosphorylation of FBP1 on Ser144 promoted breast tumor growth in vitro and in vivo. Moreover, the levels of PIM2 and pSer144-FBP1 proteins were positively correlated with each other in human breast cancer and PIM2 knockout mice.

Conclusions: Our findings revealed that phosphorylation noncanonical FBP1 by PIM2 was a novel regulator of NF-κB pathway, and highlights PIM2 inhibitors as breast cancer therapeutics.

Phosphoglycerate kinase 1 (PGK1) in cancer: A promising target for diagnosis and therapy

Phosphoglycerate kinase 1 (PGK1) is the first critical enzyme to produce ATP in the glycolytic pathway. PGK1 is not only a metabolic enzyme but also a protein kinase, which mediates the tumor growth, migration and invasion through phosphorylation some important substrates. Moreover, PGK1 is associated with poor treatment and prognosis of cancers. This manuscript reviews the structure, functions, post-translational modifications (PTMs) of PGK1 and its relationship with tumors, which demonstrates that PGK1 has indispensable value in the tumor progression. The current review highlights the important role of PGK1 in anticancer treatments.

Metabolic alterations in the tumor microenvironment and their role in oncogenesis

Metabolic reprogramming is a characteristic feature of both cancer cells and their neighbouring cells in the tumor microenvironment (TME). The latter include stroma fibroblasts and adipocytes, that respectively differentiate to become cancer associated fibroblasts (CAFs) and cancer associated adipocytes (CAAs), and infiltrated immune cells, that collaborate with the stromal cells to provide the tumor a pro-tumorigenic niche. Here we discuss the association between the reprogramming of glucose metabolism in the TME and oncogenic signaling and its reflection in the non-canonical functions of metabolic enzymes. We also discuss the non-canonical actions of oncometabolites and the contribution to oncogenesis of external metabolites that accumulate in the TME as result of crosstalk between the tumor and the TME. Special emphasis is given in this regard to lysophosphatidic acid (LPA) and adenosine, two powerful metabolites, the concentrations of which rise in the TME due to altered metabolism of the tumor and its surrounding cells, allowing their action as external signals.