Transforming Growth Factor-β: An Agent of Change in the Tumor Microenvironment, 2021, Stuelten et al.

[SNT Gatchaman]

Transforming Growth Factor-β: An Agent of Change in the Tumor Microenvironment
Stuelten, Christina H.; Zhang, Ying E.

Transforming Growth Factor-β (TGF-β) is a key regulator of embryonic development, adult tissue homeostasis, and lesion repair. In tumors, TGF-β is a potent inhibitor of early stage tumorigenesis and promotes late stage tumor progression and metastasis. Here, we review the roles of TGF-β as well as components of its signaling pathways in tumorigenesis. We will discuss how a core property of TGF-β, namely its ability to change cell differentiation, leads to the transition of epithelial cells, endothelial cells and fibroblasts to a myofibroblastoid phenotype, changes differentiation and polarization of immune cells, and induces metabolic reprogramming of cells, all of which contribute to the progression of epithelial tumors.

Link | PDF (Frontiers in Cell and Developmental Biology)

 

[Hutan]

TGF-β, which exists in three isoforms, is synthesized as a propeptide consisting of the active TGF-β and the latency associated protein (LAP). The propeptide is cleaved by furin or furin-like protease during maturation, but LAP and TGF-β remain strongly associated via non-covalent interactions. LAP is tethered to latent TGF-β binding protein (LTBP) or glycoprotein-A repetitions predominant proteins (GARPs) to form latent complexes that shield the active TGF-β and prevent it from binding to receptors (Robertson and Rifkin, 2016). As such, most of the TGF-β deposited in the extracellular space is inactive, although active TGF-β is observed in specific locations (Barcellos-Hoff et al., 1994). Bioavailability of TGF-β is additionally regulated by TGF-β-binding proteins like fibromodulin and decorin which sequester TGF-β and prevent it from binding to specific TGF-β receptors

This is interesting. So potentially some methods of measuring TGF-B, maybe the methods that chop proteins up into little bits, might not accurately report the activity capacity of the protein?

 

[SNT Gatchaman]

Some quotes that may be relevant more widely than malignancy —

TGF-β, which exists in three isoforms, is synthesized as a propeptide consisting of the active TGF-β and the latency associated protein (LAP). The propeptide is cleaved by furin or furin-like protease during maturation, but LAP and TGF- β remain strongly associated via non-covalent interactions. LAP is tethered to latent TGF-β binding protein (LTBP) or glycoprotein-A repetitions predominant proteins (GARPs) to form latent complexes that shield the active TGF-β and prevent it from binding to receptors. As such, most of the TGF-β deposited in the extracellular space is inactive, although active TGF-β is observed in specific locations.

Bioavailability of TGF- β is additionally regulated by TGF-β-binding proteins like fibromodulin and decorin which sequester TGF-β and prevent it from binding to specific TGF-β receptors. Activation of latent TGF-β is a key step in the regulation of TGF-β-signaling activity. During activation, active TGF-β is released from the latent complex by local changes in pH or shear stress

TGF-β can modulate neoangiogenesis and induce EndMT [endothelial-mesenchymal transition]. TGF-β stimulates neoangiogenesis by inducing VEGF expression in tumor and stromal cells like macrophages in a Smad3-dependent manner. Further effects of TGF-β on endothelial cells are due the presence of the TGF-β Coreceptor Endoglin.

Endoglin has an important role in regulating angiogenesis and endothelial function. Endoglin is found to be overexpressed in the tumor neovasculature of brain, lung, breast, stomach and colon. In animal models, endoglin overexpression in tumor vasculature leads to leaky vessels with an incomplete mural coverage

TGF-β affects the immune response to tumors on several levels: [...] and it regulates proliferation, differentiation and migration of immune cells. [...] leads to immunosuppression and immune evasion of tumors by changing proliferation and differentiation of residential T cells, neutrophils and macrophages, dendritic cells and NK cells. Specifically, TGF-β inhibits T-cell proliferation as well as Th1 differentiation by inhibiting IL- 2 expression, and together with other cytokines promotes Treg and Th17 differentiation [...] The polarization of immune cells can increase their capacity to activate TGF-β.

To compensate for restricted blood and nutrient supply in tumors, another property of TGF-β comes in handy: it can shift the metabolism of cells in the tumor environment [...] Early on, it was observed that TGF-β increases glucose uptake and lactate secretion of cells. TGF-β signaling is now known to affect oxidative phosphorylation, the pentose phosphate pathway, glycolysis, fatty acid oxidation, and amino acid metabolism.

In general, TGF-β shifts metabolism from mitochondrial oxidative phosphorylation toward a ketogenic metabolism, and EMT and EndMT, which are induced by TGF-β, can shift tumor and endothelial cell metabolism from oxidative phosphorylation toward anaerobic glycolysis.

Mechanistically, auto- or paracrine TGF-β signaling reduces Cav-1 expression and concomitantly CD36 expression which leads to increased ROS production and HIF-1α stabilization. HIF-1α in turn increases glycolysis and increased lactate production. [...] Lactate also has many effects on immune cells: it inhibits proliferation, cytokine production and cytotoxic activity of cytotoxic CD8 cells

In addition to its effects on energy metabolism, TGF- β-induced metabolic reprogramming of CAFs [cancer-associated fibroblasts] leads to increased reactive oxygen species (ROS) production and ROS accumulation by inactivation of CSK3 and the mitochondrial complex IV.

TGF-β-mediated metabolic reprogramming of CAFs can spread to neighboring cells. Conceivably, once triggered, large parts of the tumor stroma might convert to a “Warburg-like” cancer metabolism. This metabolic flexibility would allow CAFs and other cells to better adapt to the changing demands of the tumor microenvironment to hypoxic and aerobic zones: in the fibrotic and hypoxic tumor core, tumor cells, fibroblasts and endothelial cells can utilize glucose by anaerobic glycolysis and secrete lactate and pyruvate, while at the oxygen-rich edges of the tumor lactate and pyruvate can be taken up by tumor cells, fibroblasts and endothelial cells and entered into the citrate cycle.

 

[SNT Gatchaman]

During activation, active TGF-β is released from the latent complex by local changes in pH or shear stress

This could relate to PEM. Lowering the pH with lactic acidosis, shear stress on the ECM with activity? Do we have papers on TGF-β before and after exercise? (Especially 4, 24, 48 hours).

 

[Hutan]

Activation of latent TGF-β is a key step in the regulation of TGF-β-signaling activity. During activation, active TGF-β is released from the latent complex by local changes in pH or shear stress, TSP1-, tenascin- or integrin binding, or by proteolytic cleavage by matrix metallo- and other proteases. Of those, integrin-mediated TGF-β activation is of particular importance, and loss of integrin-mediated TGF-β1 activation mimics the phenotype of TGF-β1-null mice (Yang et al., 2007). Likewise, mice lacking αvβ6- and αvβ8-integrins mimic the abnormalities of TGF-β1- and TGF-β3-null mice (Aluwihare et al., 2009). Integrin-mediated TGF-β activation depends on the recognition and binding of LAP’s RGD motif by integrin αv. Two mechanisms of integrin-mediated TGF-β activation are known: traction force mediated release of active TGF-β, typically seen for αvβ6 integrin (Figure 1-1), and release of TGF-β by proteolytic cleavage of LAP, observed for αvβ8 integrin (Figure 1-2; Nolte and Margadant, 2020). Integrin αvβ6 is tethered to the actomyosin cytoskeleton. After binding LAP, αvβ6 integrins link the latent complex to the actomyosin cytoskeleton. Because the latent TGF-β complex is also connected to the extracellular matrix, actomyosin generated traction forces pull on and lead to conformational changes of the latent complex and release of active TGF-β (Buscemi et al., 2011; Klingberg et al., 2014; Hinz, 2015). Notably, in this model of traction force-mediated TGF-β activation the extracellular matrix provides the counterforce for actomyosin contraction; therefore, changes in matrix stiffness should affect the traction-force mediated release of TGF-β. Indeed, integrin-mediated TGF-β activation is more efficient in stiff matrix with an elastic modulus > 10 kPa than in soft matrix (Klingberg et al., 2014; Hinz, 2015; Hiepen et al., 2020). In contrast, integrin αvβ8 does not interact with the cytoskeleton and thus cannot release active TGF-β by mechanical force transduction. It instead requires a chaperone, GARP or LRRC33, and proteases such as MT1-MMP (MMP14) to proteolytically cleave LAP and release active TGF-β (Mu et al., 2002; Liénart et al., 2018).

Also interesting. Ugh, there's so much to know and remember. I think I've read and written about integrins before.

Activation of TGF- B1 by integrins is an important method of activation.
Traction force mediated release is one important mechanism of this.
One type of integrin is 'tethered to the actomyosin cytoskeleton' and it can also tether the latent TGF-B complex to the actomyosin cytoskeleton.
The TGF-B complex is also tethered to the extracellular matrix.
Actomyosin generated traction forces lead to the shape of the complex changing, and the release of the TGF-B. They note that a stiff matrix allows for more efficient TGF-B activation.

Actomyosin is a complex molecule formed by one molecule of myosin and one or two molecules of actin. In muscle, actin and myosin filaments are oriented parallel to each other and to the long axis of the muscle.

Crosspost with SNT.

 

[Hutan]

Here's an image of part of what is going on, for those of us who remember better with a picture. Sorry about the size but I think it is worth it. (I think they meant integrins, not ingretins.)

This is from a 2022 paper with the interesting title of
The Love-Hate Relationship Between TGF-β Signaling and the Immune System During Development and Tumorigenesis

The pink knuckle bone shaped molecule is the TGF-B. It's locked up by the turquoise LAP molecule. But, when the complex is anchored in a suitable environment, actomyosin contractions sort of spring the trap, causing the LAP to disintegrate (the little bits of turquoise), releasing the TGF-B. The image above shows two different ways this can happen. It is all just amazing stuff.

What relevance this has to us, if any, I do not know. But I do recall the feeling when walking up a slope or bending down and stretching my hamstrings, that rapid and unnatural feeling of fatigue in the muscle. I wonder what it feels like to have TGF-B released in muscle. Could it act that fast?

 

[SNT Gatchaman]

They note that a stiff matrix allows for more efficient TGF-B activation.

Which might relate to the sometimes comorbid "hypermobile EDS". From Fascial thickness and stiffness in hypermobile Ehlers-Danlos syndrome (2022, Am J Med Genetics, paywall) —

[Sternocleidomastoid] deep fascia thickness in non-hEDS subjects without neck pain (1.3 ± 0.2 mm) or with neck pain (1.5 ± 0.3 mm) were consistent with the prior report of abnormal values >1.5 mm (A. Stecco et al., 2014). hEDS patients had greater mean SCM deep fascia thickness (1.8 ± 0.3 mm) compared with non-hEDS patients with neck pain, suggesting an amplified laydown of ECM.

The excess laydown of ECM may occur in response to inflammation. The phenotypic presentation of hEDS is wide and is associated with multiple inflammatory-like conditions and symptoms. Proteomic studies in hEDS showed dysregulated expression of genes involved in inflammation, pain, and immune responses in the ECM environment. Pathologic fibroblast-to-myofibroblast transition was present and prevalent and associated with augmented levels of inflammatory mediators including metalloproteinase-9.

Deep fascia densification is also associated with alteration in gliding properties. [...] These alterations of gliding interactions may influence joint mobility and lead to impaired biomechanics, altered alignment, proprioceptive dysfunction, pain, and predisposition to future injuries.

 

[SNT Gatchaman]

See also Are the integrin binding motifs within SARS CoV-2 spike protein and MHC class II alleles playing the key role in COVID-19? (2023)