Effect of endogenous phenoloxidase on protein solubility and digestibility after processing of Tenebrio molitor, Alphitobius diaperinus and Hermetia illucens.

Upon extracting soluble proteins from insects as potential food ingredient, endogenous enzymes, such as phenoloxidases, are expected to negatively affect protein properties. The effect of phenoloxidases on solubility and digestibility of proteins was investigated for larvae of Tenebrio molitor, Alphitobius diaperinus and Hermetia illucens. Phenoloxidase inhibition was done using blanching (50 s, 90 °C) before extraction or extracting in presence of sulfite. Similar soluble protein yields and compositions were found without and with sulfite addition, whereas blanching decreased soluble protein yield. Upon in-vitro hydrolysis by pepsin and trypsin, soluble proteins from H. illucens were more digestible than those of T. molitor and A. diaperinus. Phenoloxidase activity during grinding negatively affected in-vitro pepsin hydrolysis. Besides phenoloxidase activity, also endogenous proteases were shown to remain active at pH 8 in extracts containing sulfite and after blanching of larvae. This stresses that protease activity needs to be carefully controlled in the design of insect based ingredients.

microRNA-155, induced by interleukin-1ß, represses the expression of microphthalmia-associated transcription factor (MITF-M) in melanoma cells.

Loss of expression of surface antigens represents a significant problem for cancer immunotherapy. Microphthalmia-associated transcription factor (MITF-M) regulates melanocyte fate by driving expression of many differentiation genes, whose protein products can be recognized by cytolytic T lymphocytes. We previously reported that interleukin-1ß (IL-1ß) can downregulate MITF-M levels. Here we show that downregulation of MITF-M expression by IL-1ß was paralleled by an upregulation of miR-155 expression in four melanoma lines. We confirmed that miR-155 was able to target endogenous MITF-M in melanoma cells and demonstrated a role for miR-155 in the IL-1ß-induced repression of MITF-M by using an antagomiR. Notably, we also observed a strong negative correlation between MITF-M and miR-155 levels in a mouse model of melanoma. Taken together, our results indicate that MITF-M downregulation by inflammatory stimuli might be partly due to miR-155 upregulation. This could represent a novel mechanism of melanoma immune escape in an inflammatory microenvironment.

Interleukins 1alpha and 1beta secreted by some melanoma cell lines strongly reduce expression of MITF-M and melanocyte differentiation antigens.

We report that melanoma cell lines expressing the interleukin-1 receptor exhibit 4- to 10-fold lower levels of mRNA of microphthalmia-associated transcription factor (MITF-M) when treated with interleukin-1beta. This effect is NF-kappaB and JNK-dependent. MITF-M regulates the expression of melanocyte differentiation genes such as MLANA, tyrosinase and gp100, which encode antigens recognized on melanoma cells by autologous cytolytic T lymphocytes. Accordingly, treating some melanoma cells with IL-1beta reduced by 40-100% their ability to activate such antimelanoma cytolytic T lymphocytes. Finally, we observed large amounts of biologically active IL-1alpha or IL-1beta secreted by two melanoma cell lines that did not express MITF-M, suggesting an autocrine MITF-M downregulation. We estimate that approximately 13% of melanoma cell lines are MITF-M-negative and secrete IL-1 cytokines. These results indicate that the repression of melanocyte-differentiation genes by IL-1 produced by stromal cells or by tumor cells themselves may represent an additional mechanism of melanoma immune escape.