Implication of integrins α3β1 and α5β1 in invasion and anoikis of SK-Mel-147 human melanoma cells: non-canonical functions of protein kinase Akt

Development of anoikis-related long non-coding RNA signature associated with prognosis and immune landscape in cutaneous melanoma patients

BACKGROUND

Anoikis is involved in many critical biological processes in tumors; however, function in CM is still unknown. In this study, the relevance between Anoikis-related lncRNAs (ARLs) and the clinicopathological characteristics of patients with CM was comprehensively assessed.

METHODS

Through analysis of TCGA dataset, ARLs were identified by using TCGA dataset. Based on the ARLs, a risk model was established to anticipate the prognosis of patients with CM, besides, the prediction accuracy of the model was evaluated. The immune infiltration landscape of patients with CM was assessed comprehensively, and the correlation between ARLs and immunity was elucidated. Immunotherapy and drug sensitivity analyses were applied to analyze the treatment response in patients with CM with diverse risk scores. Different subgroups were distinguished among the patients using consensus cluster analysis.

RESULTS

A risk model based on six ARLs was set up to obtain an accurate prediction of the prognosis of patients with CM. There were distinctions in the immune landscape among CM patients with diverse risk scores and subgroups. Six prognosis-related ARLs were highly correlated with the number of immune cells. Patients with CM with different risk scores have various sensitivities to immunotherapy and antitumor drug treatments.

CONCLUSION

Our newly risk model associated with ARLs has considerable prognostic value for patients with CM. Not only has the risk model high prediction accuracy but it also indicates the immune status of CM patients, which will provide a new direction for the individualized therapy of patients with CM.

Implication of integrin α5β1 in senescence of SK-Mel-147 human melanoma cells

Downregulation of α5β1 integrin in the SK-Mel-147 human melanoma culture model sharply inhibits the phenotypic manifestations of tumor progression: cell proliferation and clonal activity. This was accompanied by a 2-3-fold increase in the content of SA-β-Gal positive cells thus indicating an increase in the cellular senescence phenotype. These changes were accompanied by a significant increase in the activity of p53 and p21 tumor suppressors and components of the PI3K/Akt/mTOR/p70 signaling pathway. Pharmacological inhibition of mTORC1 reduced the content of SA-β-Gal positive cells in the population of α5β1-deficient SK-Mel-147 cells. A similar effect was observed with pharmacological and genetic inhibition of the activity of Akt1, one of the three Akt protein kinase isoenzymes; suppression of other Akt isozymes did not affect melanoma cell senescence. The results presented in this work and previously obtained indicate that α5β1 shares with other integrins of the β1 family the function of cell protection from senescence. This function is realized via regulation of the PI3K/Akt1/mTOR signaling pathway, in which Akt1 exhibits a non-canonical activity.

Therapeutic targeting of anoikis resistance in cutaneous melanoma metastasis

The acquisition of resistance to anoikis, the cell death induced by loss of adhesion to the extracellular matrix, is an absolute requirement for the survival of disseminating and circulating tumour cells (CTCs), and for the seeding of metastatic lesions. In melanoma, a range of intracellular signalling cascades have been identified as potential drivers of anoikis resistance, however a full understanding of the process is yet to be attained. Mechanisms of anoikis resistance pose an attractive target for the therapeutic treatment of disseminating and circulating melanoma cells. This review explores the range of small molecule, peptide and antibody inhibitors targeting molecules involved in anoikis resistance in melanoma, and may be repurposed to prevent metastatic melanoma prior to its initiation, potentially improving the prognosis for patients.

Integrin alpha9 emerges as a key therapeutic target to reduce metastasis in rhabdomyosarcoma and neuroblastoma

The majority of current cancer therapies are aimed at reducing tumour growth, but there is lack of viable pharmacological options to reduce the formation of metastasis. This is a paradox, since more than 90% of cancer deaths are attributable to metastatic progression. Integrin alpha9 (ITGA9) has been previously described as playing an essential role in metastasis; however, little is known about the mechanism that links this protein to this process, being one of the less studied integrins. We have now deciphered the importance of ITGA9 in metastasis and provide evidence demonstrating its essentiality for metastatic dissemination in rhabdomyosarcoma and neuroblastoma. However, the most translational advance of this study is to reveal, for the first time, the possibility of reducing metastasis by pharmacological inhibition of ITGA9 with a synthetic peptide simulating a key interaction domain of ADAM proteins, in experimental metastasis models, not only in childhood cancers but also in a breast cancer model.

[Integrin α3β1 signaling in regulation of the SK-Mel-147 melanoma cell senescence]

Using a model of the human SK-Mel-147 melanoma cell line, it was shown that blocking the expression of integrin α3β1 by transduction of cells with α3-specific shRNA did not affect their proliferation, but sharply increased the proportion of SA-β-Gal-positive cells, a phenotypic feature of cell senescence. These findings were accompanied by a significant increase in the activity of the Akt and mTOR protein kinases and the expression of p53 and p21 oncosupressors. Pharmacological inhibition of mTORC1 reduced the number SA-β-Gal-positive cells in the SK-Mel-147 cell population depleted of α3β1. Based on our recent data on a non-canonical function of Akt isomers in the regulation of SK-Mel-147 cell senescence caused by deficiency of α2β1 receptor, we investigated the role of Akt isomers in senescence induced by the α3β1 knockdown. It appeared that in the cell population with downregulated α3β1, inhibition of Akt1 reduced the number SA-β-Gal positive cells to the level of control cell population, while inhibition of Akt2 had no visible effect. Our results demonstrate that the laminin-specific integrin α3β1, like the collagen-specific receptor α2β1, is involved in tumor cell protection from senescence, and senescence induced by α3β1 depletion, like that caused by α2β1 deficiency, is based on a signaling mechanism employing a non-canonical function of the Akt1 isoform.

Implication of integrin α2β1 in senescence of SK-Mel-147 human melanoma cells

This investigation addressed the impact of integrin-initiated signaling pathways on senescence of tumor cells. In a model of human SK-Mel-147 melanoma cells, the silencing of integrin α2β1 strongly reduced cell proliferation and enhanced the percentage of SA-β-Gal-positive cells, a phenotypic feature of cellular senescence. These changes were accompanied by a significant increase in the activity of Akt and mTOR protein kinases and also in the expression of p53 and p21 oncosuppressors. Pharmacological inhibition of Akt and mTORC1 and genetic inhibition of p53 and p21 reduced the senescence of α2β1-depleted SK-Mel-147 cells to the level of control cells. Based on our earlier data on the non-canonical functions of Akt isomers in the invasion and anoikis of SK-Mel-147 cells, we investigated the role of Akt isomers in senescence induced by α2β1 suppression. The inhibition of Akt1 strongly reduced the percentage of SA-β-Gal-positive cells in the α2β1-depleted cell population, while the inhibition of Akt2 did not have a noticeable effect. Our data demonstrated for the first time that α2β1 is involved in the protection of tumor cells against senescence and that senescence, which is induced by the downregulation of α2β, is based on a signaling mechanism in which Akt1 performs a non-canonical function.