From Science Daily
Date: September 18, 2017
Source: Salk Institute
Summary: Researchers have discovered how oxygen-deprived tumors survive body’s immune response, explains a new report.
The immune system automatically destroys dysfunctional cells such as cancer cells, but cancerous tumors often survive nonetheless. A new study by Salk scientists shows one method by which fast-growing tumors evade anti-tumor immunity.
The Salk team uncovered two gene-regulating molecules that alter cell signaling within tumor cells to survive and subvert the body’s normal immune response, according to a September 18, 2017, paper in Nature Cell Biology. The discovery could one day point to a new target for cancer treatment in various types of cancer.
“The immunological pressure occurring during tumor progression might be harmful for the tumor to prosper,” says Salk Professor Juan Carlos Izpisua Belmonte, senior author of the work and holder of the Roger Guillemin Chair. “However, the cancer cells find a way to evade such a condition by restraining the anti-tumor immune response.”
Cancerous tumors often grow so fast that they use up their available blood supply, creating a low-oxygen environment called hypoxia. Cells normally start to self-destruct under hypoxia, but in some tumors, the microenvironment surrounding hypoxic tumor tissue has been found to help shield the tumor.
“Our findings actually indicate how cancer cells respond to a changing microenvironment and suppress anti-tumor immunity through intrinsic signaling,” says Izpisua Belmonte. The answer was through microRNAs.
MicroRNAs — small, noncoding RNA molecules that regulate genes by silencing RNA — have increasingly been implicated in tumor survival and progression. To better understand the connection between microRNAs and tumor survival, the researchers screened different tumor types for altered levels of microRNAs. They identified two microRNAs — miR25 and miR93 — whose levels increased in hypoxic tumors.
The team then measured levels of those two microRNAs in the tumors of 148 [human] cancer patients and found that tumors with high levels of miR25 and miR93 led to a worse prognosis in patients compared to tumors with lower levels. The reverse was true for another molecule called cGAS: the lower the level of cGAS in a tumor, the worse the prognosis for the patient.
Previous research has shown that cGAS acts as an alarm for the immune system by detecting mitochondrial DNA floating around the cell — a sign of tissue damage — and activating the body’s immune response.
“Given these results, we wondered if these two microRNA molecules, miR25 and miR93, could be lowering cGAS levels to create a protective immunity shield for the tumor,” says Min-Zu (Michael) Wu, first author of the paper and a research associate in Salk’s Gene Expression Laboratory.
That is exactly what the team confirmed with further experiments. Using mouse models and tissue samples, the researchers found that a low-oxygen (hypoxia) state triggered miR25 and miR93 to set off a chain of cell signaling that ultimately lowered cGAS levels. If the researchers inhibited miR25 and miR93 in tumor cells, then cGAS levels remained high in low-oxygen (hypoxic) tumors.
Researchers could slow tumor growth in mice if they inhibited miR25 and miR93. Yet, in immune-deficient mice, the effect of inhibiting miR25 and miR93 was diminished, further indicating that miR25 and miR93 help promote tumor growth by influencing the immune system.
Identifying miR25 and miR93 may help researchers pinpoint a good target to try to boost cGAS levels and block tumor evasion of the immune response. However, the team says directly targeting microRNA in treatment can be tricky. Targeting the intermediate players in the signaling between the two microRNAs and cGAS may be easier.
“To follow up this study, we’re now investigating the different immune cells that can contribute to cancer anti-tumor immunity,” adds Wu.
Materials provided by Salk Institute.
Kobayashi M1, Saito A, Tanaka Y, Michishita M, Kobayashi M, Irimajiri M, Kaneda T, Ochiai K, Bonkobara M, Takahashi K, Hori T, Kawakami E.
Canine prostate cancer (cPCa) is an untreatable malignant neoplasm resulting in local tissue invasion and distant metastasis. MicroRNAs (miRs) are small non-coding RNAs that function as oncogenes or tumor suppressors. The purpose of this study was to characterize the expression of miRs that are altered in cPCa tissue. The expression levels of 277 mature miRs in prostatic tissue (n=5, respectively) were compared between the non-tumor and tumor groups using real-time PCR. Five miRs (miR-18a, 95, 221, 222 and 330) were up-regulated, but 14 miRs (miR-127, 148a, 205, 299, 329b, 335, 376a, 376c, 379, 380, 381, 411, 487b and 495) were down-regulated specifically in cPCa (P<0.05). These miRs have potential use as early diagnosis markers for cPCa and in miR-based therapy.
MicroRNA expression in canine mammary cancer
MicroRNAs (miRNAs) are 18-22-nt noncoding RNAs that are involved in post-transcriptional regulation of genes. Oncomirs, a subclass of miRNAs, include genes whose expression, or lack thereof, are associated with cancers. Until the last decade, the domestic dog was an underused model for the study of various human diseases that have genetic components. The dog exhibits marked genetic and physiologic similarity to the human, thereby making it an excellent model for study and treatment of various hereditary diseases. Furthermore, because the dog presents with distinct, spontaneously occurring mammary tumors, it may serve as a model for genetic analysis and treatments of humans with malignant breast tumors. Because miRNAs have been found to act as both tumor suppressors and oncogenes in several different cancers, expression patterns of ten miRNAs (miR-15a, miR-16, miR-17-5p, miR-21, miR-29b, miR-125b, miR-145, miR-155, miR-181b, let-7f) known to be associated with human breast cancers were compared to malignant canine mammary tumors (n = 6) and normal canine mammary tissue (n = 10). Resulting data revealed miR-29b and miR-21 to have a statistically significant (p < 0.05 by MANOVA analysis) upregulation in cancerous samples. The ten canine miRNAs follow the same pattern of expression as in the human, except for miR-145 which does not show a difference in expression between the normal and cancerous canine samples. In addition, when analyzed according to specific cancer phenotypes, miR-15a and miR-16 show a significant downregulation in canine ductal carcinomas while miRsR-181b, -21, -29b, and let-7f show a significant upregulation in canine tubular papillary carcinomas.
MicroRNA expression in canine mammary cancer. Available from: https://www.researchgate.net/publication/23135972_MicroRNA_expression_in_canine_mammary_cancer [accessed Sep 20, 2017].
MicroRNA-214 Promotes Apoptosis in Canine Hemangiosarcoma by Targeting the COP1-p53 Axis
MicroRNA-214 regulates both angiogenic function in endothelial cells and apoptosis in various cancers. However, the regulation and function of miR-214 is unclear in canine hemangiosarcoma, which is a spontaneous model of human angiosarcoma. The expression and functional roles of miR-214 in canine hemangiosarcoma were presently explored by performing miRNA TaqMan qRT-PCR and transfecting cells with synthetic microRNA. Here, we report that miR-214 was significantly down-regulated in the cell lines used and in clinical samples of canine hemangiosarcoma. Restoration of miR-214 expression reduced cell growth and induced apoptosis in canine hemangiosarcoma cell lines through transcriptional activation of p53-regulated genes although miR-214 had a slight effect of growth inhibition on normal endothelial cells. We identified COP1, which is a critical negative regulator of p53, as a novel direct target of miR-214. COP1 was overexpressed and the specific COP1 knockdown induced apoptosis through transcriptional activation of p53-regulated genes as well as did miR-214-transfection in HSA cell lines. Furthermore, p53 knockdown abolished the miR-214-COP1-mediated apoptosis; thus, miR-214 and COP1 regulated apoptosis through controlling p53 in HSA. In conclusion, miR-214 functioned as a tumor suppressor in canine hemangiosarcoma by inducing apoptosis through recovering the function of p53. miR-214 down-regulation and COP1 overexpression is likely to contribute to tumorigenesis of HSA. Therefore, targeting miR-214-COP1-p53 axis would possibly be a novel effective strategy for treatment of canine hemangiosarcoma and capable of being applied to the development of novel therapeutics for human angiosarcoma.