The nuclear membrane serves a critical role in protecting the contents of the nucleus and facilitating material and signal exchange between the nucleus and cytoplasm. While extensive research has been dedicated to topics such as nuclear membrane assembly and disassembly during cell division, as well as interactions between nuclear transmembrane proteins and both nucleoskeletal and cytoskeletal components, there has been comparatively less emphasis on exploring the regulation of nuclear morphology through nuclear membrane integrity. In particular, the role of type II integral proteins, which also function as transcription factors, within the nuclear membrane remains an area of research that is yet to be fully explored. The integrity of the nuclear membrane is pivotal not only during cell division but also in the regulation of gene expression and the communication between the nucleus and cytoplasm. Importantly, it plays a significant role in the development of various diseases. This review paper seeks to illuminate the biomolecules responsible for maintaining the integrity of the nuclear membrane. It will delve into the mechanisms that influence nuclear membrane integrity and provide insights into the role of type II membrane protein transcription factors in this context. Understanding these aspects is of utmost importance, as it can offer valuable insights into the intricate processes governing nuclear membrane integrity. Such insights have broad-reaching implications for cellular function and our understanding of disease pathogenesis.

Cancer cells often exhibit resistance to apoptotic cell death, but they may be vulnerable to other types of cell death. Elucidating additional mechanisms that govern cancer cell death is crucial for developing new therapies. Our research identified cyclic AMP-responsive element-binding protein 3 (CREB3) as a crucial regulator and initiator of a unique cell death mechanism known as karyoptosis. This process is characterized by nuclear shrinkage, deformation, and the loss of nuclear components following nuclear membrane rupture. We found that the N-terminal domain (aa 1-230) of full-length CREB3 (CREB3-FL), which is anchored to the nuclear inner membrane (INM), interacts with lamins and chromatin DNA. This interaction maintains a balance between the outward force exerted by tightly packed DNA and the inward constraining force, thereby preserving INM integrity. Under endoplasmic reticulum (ER) stress, aberrant cleavage of CREB3-FL at the INM leads to abnormal accumulation of the cleaved form of CREB3 (CREB3-CF). This accumulation disrupts the attachment of CREB3-FL to the INM, resulting in sudden rupture of the nuclear membrane and the onset of karyoptosis. Proteomic studies revealed that CREB3-CF overexpression induces a DNA damage response akin to that caused by UVB irradiation, which is associated with cellular senescence in cancer cells. These findings demonstrated that the dysregulation of CREB3-FL cleavage is a key factor in karyoptotic cell death. Consequently, these findings suggest new therapeutic strategies in cancer treatment that exploit the process of karyoptosis.

Cyclic guanosine-adenosine monophosphate synthase (cGAS) is a key cytosolic DNA sensor that plays a pivotal role in the innate immune response. Although a decade of research on the cGAS has advanced our understanding of inflammasome formation, cytokine production, and signaling pathways, the role of cGAS in the nucleus remains unclear. In this study, we found that the nuclear localization of endogenous and stably expressed cGAS differed from transiently expressed cGAS, which mainly localized in the cytosol. In the nucleus, cGAS is tightly bound to chromatin DNA. The chromatin DNA binding of cGAS was dependent on RSK2. Our molecular mechanism study indicated that the N-lobe of RSK2 harboring 1–323 interacted with the NTase domain of cGAS harboring residues 213–330. This interaction increased RSK2-induced cGAS phosphorylation at Ser120 and Thr130, resulting in the tightly binding of cGAS to chromatin. Importantly, epidermal growth factor (EGF)-induced cell transformation and anchorage-independent colony growth showed an increase in growth factors, such as EGF or bFGF, in cGAS stable expression compared to mock expression. Notably, the cGAS-S120A/T130A mutant abolished the increasing effect of cell transformation of JB6 Cl41 cells and colony growth of SK-MEL-2 malignant melanoma cells. The results suggested that cGAS’s chromatin DNA binding, which is indispensable to RSK2-dependent phosphorylation of cGAS at Ser120/Thr130, provides the first clue to how cGAS may participate in chromatin remodeling in the nucleus.

Weidong Chen, Ga-Eun Lee, Dohyun Jeung, Jiin Byun, Wu Juan, Yong-Yeon Cho. J Cancer Prev 2023;28:143-9. https://doi.org/10.15430/JCP.2023.28.4.143