Molecular mechanism of the "feedback loop" model of carcinogenesis

Sirtuins as Key Regulators in Pancreatic Cancer: Insights into Signaling Mechanisms and Therapeutic Implications

Pancreatic ductal adenocarcinoma (PDAC) stands as one of the most lethal cancers, marked by rapid progression, pronounced chemoresistance, and a complex network of genetic and epigenetic dysregulation. Within this challenging context, sirtuins, NAD+-dependent deacetylases, have emerged as pivotal modulators of key cellular processes that drive pancreatic cancer progression. Each sirtuin contributes uniquely to PDAC pathogenesis. SIRT1 influences apoptosis and chemoresistance through hypoxia, enhancing glycolytic metabolism and HIF-1α signaling, which sustain tumor survival against drugs like gemcitabine. SIRT2, conversely, disrupts cancer cell proliferation by inhibiting eIF5A, while SIRT3 exerts tumor-suppressive effects by regulating mitochondrial ROS and glycolysis. SIRT4 inhibits aerobic glycolysis, and its therapeutic upregulation has shown promise in curbing PDAC progression. Furthermore, SIRT5 modulates glutamine and glutathione metabolism, offering an avenue to disrupt PDAC's metabolic dependencies. SIRT6 and SIRT7, through their roles in angiogenesis, EMT, and metastasis, represent additional targets, with modulators of SIRT6, such as JYQ-42, showing potential to reduce tumor invasiveness. This review aims to provide a comprehensive exploration of the emerging roles of sirtuins, a family of NAD+-dependent enzymes, as critical regulators within the oncogenic landscape of pancreatic cancer. This review meticulously explores the nuanced involvement of sirtuins in pancreatic cancer, elucidating their contributions to tumorigenesis and suppression through mechanisms such as metabolic reprogramming, the maintenance of genomic integrity and epigenetic modulation. Furthermore, it emphasizes the urgent need for the development of targeted therapeutic interventions aimed at precisely modulating sirtuin activity, thereby enhancing therapeutic efficacy and optimizing patient outcomes in the context of pancreatic malignancies.

Biology of cancer; from cellular and molecular mechanisms to developmental processes and adaptation

Cancer research has been largely focused on the cellular and molecular levels of investigation. Recent data show that not only the cell but also the extracellular matrix plays a major role in the progression of malignancy. In this way, the cells and the extracellular matrix create a specific local microenvironment that supports malignant development. At the same time, cancer implies a systemic evolution which is closely related to developmental processes and adaptation. Consequently, there is currently a real gap between the local investigation of cancer at the microenvironmental level, and the pathophysiological approach to cancer as a systemic disease. In fact, the cells and the matrix are not only complementary structures but also interdependent components that act synergistically. Such relationships lead to cell-matrix integration, a supracellular form of biological organization that supports tissue development. The emergence of this supracellular level of organization, as a structure, leads to the emergence of the supracellular control of proliferation, as a supracellular function. In humans, proliferation is generally involved in developmental processes and adaptation. These processes suppose a specific configuration at the systemic level, which generates high-order guidance for local supracellular control of proliferation. In conclusion, the supracellular control of proliferation act as an interface between the downstream level of cell division and differentiation, and upstream level of developmental processes and adaptation. Understanding these processes and their disorders is useful not only to complete the big picture of malignancy as a systemic disease, but also to open new treatment perspectives in the form of etiopathogenic (supracellular or informational) therapies.

LncRNAs driving feedback loops to boost drug resistance: sinuous pathways in cancer

Feedback loops mediate signaling pathways to maintain cellular homeostasis. There are two types, positive and negative feedback loops. Both are subject to alterations, and consequently can become pathogenic in the development of diseases such as cancer. Long noncoding RNAs (lncRNAs) are regulators of signaling pathways through feedback loops hidden as the dark regulatory elements yet to be described with great impact on cancer tumorigenesis, development, and drug resistance. Several feedback loops have been studied in cancer, however, how they are regulated by lncRNAs is hardly evident, setting a trending topic in oncological research. In this review, we recapitulate and discuss the feedback loops that are regulated by lncRNAs to promote drug resistance. Furthermore, we propose additional strategies that allow us to identify, analyze and comprehend feedback loops regulated by lncRNAs to induce drug resistance or even to gain insight into novel feedback loops that are stimulated under the pressure of treatment and consequently increase its efficacy. This knowledge will be useful to optimize the therapeutic use of oncological drugs.

Signaling pathways in intestinal homeostasis and colorectal cancer: KRAS at centre stage

The intestinal epithelium acts as a physical barrier that separates the intestinal microbiota from the host and is critical for preserving intestinal homeostasis. The barrier is formed by tightly linked intestinal epithelial cells (IECs) (i.e. enterocytes, goblet cells, neuroendocrine cells, tuft cells, Paneth cells, and M cells), which constantly self-renew and shed. IECs also communicate with microbiota, coordinate innate and adaptive effector cell functions. In this review, we summarize the signaling pathways contributing to intestinal cell fates and homeostasis functions. We focus especially on intestinal stem cell proliferation, cell junction formation, remodelling, hypoxia, the impact of intestinal microbiota, the immune system, inflammation, and metabolism. Recognizing the critical role of KRAS mutants in colorectal cancer, we highlight the connections of KRAS signaling pathways in coordinating these functions. Furthermore, we review the impact of KRAS colorectal cancer mutants on pathway rewiring associated with disruption and dysfunction of the normal intestinal homeostasis. Given that KRAS is still considered undruggable and the development of treatments that directly target KRAS are unlikely, we discuss the suitability of targeting pathways downstream of KRAS as well as alterations of cell extrinsic/microenvironmental factors as possible targets for modulating signaling pathways in colorectal cancer.