The many functions of phosphoinositides in cytosolic signaling were extensively studied; however, their activities in the cell nucleus are much less clear. In this review, we summarize data about their nuclear localization and metabolism, and review the available literature on their involvements in chromatin remodeling, gene transcription, and RNA processing. We discuss the molecular mechanisms via which nuclear phosphoinositides, in particular phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), modulate nuclear processes. We focus on PI(4,5)P2’s role in the modulation of RNA polymerase I activity, and functions of the nuclear lipid islets—recently described nucleoplasmic PI(4,5)P2-rich compartment involved in RNA polymerase II transcription. In conclusion, the high impact of the phosphoinositide–protein complexes on nuclear organization and genome functions is only now emerging and deserves further thorough studies.

The kinase LCK and CD4/CD8 co-receptors are crucial components of the T cell antigen receptor (TCR) signaling machinery, leading to key T cell fate decisions. Despite decades of research, the roles of CD4–LCK and CD8–LCK interactions in TCR triggering in vivo remain unknown. In this study, we created animal models expressing endogenous levels of modified LCK to resolve whether and how co-receptor-bound LCK drives TCR signaling. We demonstrated that the role of LCK depends on the co-receptor to which it is bound. The CD8-bound LCK is largely dispensable for antiviral and antitumor activity of cytotoxic T cells in mice; however, it facilitates CD8+ T cell responses to suboptimal antigens in a kinase-dependent manner. By contrast, the CD4-bound LCK is required for efficient development and function of helper T cells via a kinase-independent stabilization of surface CD4. Overall, our findings reveal the role of co-receptor-bound LCK in T cell biology, show that CD4- and CD8-bound LCK drive T cell development and effector immune responses using qualitatively different mechanisms and identify the co-receptor–LCK interactions as promising targets for immunomodulation.

Even though the majority of knowledge about phospholipids comes from their cytoplasmic functions, in the last decade, it has been shown that nuclear phospholipids and their building blocks, inositol phosphates, have many important roles in the cell nucleus. There are clear connections of phospholipids with the regulation of gene expression and chromatin biology, however, this review focuses on less known functions of nuclear phospholipids in connection with the epigenome regulation. In particular, we highlight the roles of nuclear phospholipids and inositol phosphates that involve histone modifications, such as acetylation or methylation, tightly connected with the cell physiology. This demonstrates the importance of nuclear phospholipids in the regulation of cellular processes, and should encourage further research of nuclear phospholipids and inositol phosphates.

Relative differences in T‐cell self‐reactivity result in different T‐cell fate decisions during homeostasis and during inflammation. Numerous studies have shown that different levels of self‐reactivity shape outcomes of immune responses in both CD4+ and CD8+ T‐cell populations. Here we discuss recent advances related to T‐cell self‐reactivity and their potential implications in further basic and applied research.