β-thymosins in cancer: implications for the clinic

Immunoreactivity for thymosin beta 4 and thymosin beta 10 in the adult rat oro-gastro-intestinal tract

Thymosin beta 4 (Tβ4) and thymosin beta 10 (Tβ10) are two members of the β-thymosin family, involved in multiple cellular activities in different organs in multiple animal species. Here we report the expression pattern of Tβ4 and Tβ10 in rat tissues, in the gut and in annexed glands. The two peptide were differently expressed: Tβ4 was absent in salivary glands whereas Tβ10 was expressed in parotid and in submandibular glands. Tβ4 was mildly expressed in the tongue and in the esophagus, where Tβ10 was absent. A similar expression was found in the stomach, ileum and colon mucosa. In pancreas Tβ4 reactivity was restricted to the Langerhans islet cells; Tβ4 was also detected in the exocrine cells. Both peptide were not expressed in liver cells. When the rat expression pattern in rat organs was compared to reactivity for Tβ4 and Tβ10 in humans, marked differences were found. Our data clearly indicate a species-specific expression of Tβ4 and Tβ10, characterized by the actual unpredictability of the expression of these peptides in different cells and tissues. The common high expression of Tβ4 in mast cells, both in humans and in rats, represents one of the few similarities between these two species.

Thymosin β 4 in colorectal cancer is localized predominantly at the invasion front in tumor cells undergoing epithelial mesenchymal transition

OBJECTIVE

Thymosin β 4 (Tβ(4)) is a ubiquitous peptide that plays pivotal roles in the cytoskeletal system and in cell differentiation during embryogenesis. Recently, a role for Tβ(4) has been proposed in experimental and human carcinogenesis. This study was aimed at evaluating the correlation between Tβ(4) immunoractivity and colorectal cancer, with particular attemption to tumor cells undergoing epithelial-mesenchymal transition.

METHODS AND RESULTS

86 intestinal biopsies were retrospectively analyzed including 76 colorectal adenocarcinomas with evident features of epithelial-mesenchymal transition, and 10 samples of normal colorectal mucosa. Paraffin sections were immunostained for Tβ(4) and for E-cadherin. Total RNA was isolated from frozen specimens obtained, at surgery, from the normal colon mucosa, the deeper regions and the superficial tumor regions in four cases of colon cancer. Tβ(4) immunoreactivity was detected in the vast majority (59/76) of colon carcinomas, showing a patchy distribution, with well differentiated areas significantly more reactive than the less differentiated tumor zones. We also noted a zonal pattern in the majority of tumors, characterized by a progressive increase in immunostaining for Tβ(4) from the superficial toward the deepest tumor regions. The strongest expression for Tβ(4) was frequently detected in invading tumor cells with features of epithelial-mesenchymal transition. The increase in reactivity for Tβ(4) matched with a progressive decrease in E-cadherin expression in invading cancer cells. At mRNA level, the differences in Tβ(4) expression between the surrounding colon mucosa and the tumors samples were not significant.

CONCLUSIONS

Our data show that Tβ(4) is expressed in the majority of colon cancers, with preferential immunoreactivity in deep tumor regions. The preferential expression of the peptide and the increase in intensity of the immunostaining at the invasion front suggests a possible link between the peptide and the process of epithelial mesenchymal transition, suggesting a role for Tβ(4) in colorectal cancer invasion and metastasis.

UPLC-ESI-MS analysis of thymosins β4 and β10 in cell lysates: a simple, rapid and sensitive quantification method

Fast and reproducible quantification of thymosins β4 and β10 in different cell cultures was achieved by ultra high performance liquid chromatography coupled to mass spectrometry. We demonstrated that cancer cell lines all exhibit a higher amount of Tβ10 compared to control cells, whereas the level of Tβ4 is drastically depending on cell lines.

Regenerative protein thymosin beta-4 is a novel regulator of purinergic signaling

By an unknown mechanism, β-thymosins are extracellular modulators of angiogenesis, inflammation, wound healing, and development. We were interested in identifying β-thymosin interactors and determining their importance in β-thymosins signaling in human vein endothelial cells (HUVECs). We performed pulldown experiments with biotinylated thymosin β-4 (Tβ4) in comparison to neutravidin beads alone and used mass spectrometric analysis to identify differentially interacting proteins. By this method, we identified F1-F0 ATP synthase, a known target of antiangiogenic angiostatin. By surface plasmon resonance, we determined for Tβ4 binding to the β subunit of ATP synthase a K(D) of 12 nM. Blocking antibodies and antagonists (oligomycin, IC(50) ∼1.8 μM; piceatannol, IC(50) ∼1.05 μM; and angiostatin, IC(50) ∼2.9 μg/ml) of ATP synthase inhibited the Tβ4-induced increase in cell surface ATP levels, as measured by luciferase assay, and the Tβ4-induced increase in HUVEC migration, as measured by transwell migration assay. Silencing of the ATP-responsive purinergic receptor P2X4 with siRNA also blocked Tβ4-induced HUVEC migration in a transwell assay. Furthermore, in silico we identified common amphiphilic α-helical structural similarities between β-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis. In summary, we have identified an extracellular signaling pathway where Tβ4 increases cell surface ATP levels via ATP synthase and have shown further that ATP-responsive P2X4 receptor is required for Tβ4-induced HUVEC migration.