Cell-cell fusions and cell-in-cell phenomena in healthy cells and cancer: Lessons from protists and invertebrates

Herein we analyze two special routes of the multinucleated cells' formation - the fusion of mononuclear cells and the formation of cell-in-cell structures - in the healthy tissues and in tumorigenesis. There are many theories of tumorigenesis based on the phenomenon of emergence of the hybrid cancer cells. We consider the phenomena, which are rarely mentioned in those theories: namely, cellularization of syncytium or coenocytes, and the reversible or irreversible somatogamy. The latter includes the short-term and the long-term vegetative (somatic) cells' fusions in the life cycles of unicellular organisms. The somatogamy and multinuclearity have repeatedly and independently emerged in various groups of unicellular eukaryotes. These phenomena are among dominant survival and biodiversity sustaining strategies in protists and we admit that they can likely play an analogous role in cancer cells.

Cardiomyocyte nuclearity and ploidy: when is double trouble?

Considerable effort has gone into investigating mechanisms that underlie the developmental transition in which mammalian cardiomyocytes (CMs) switch from being able to proliferate during development, to essentially having lost that ability at maturity. This problem is interesting not only for scientific curiosity, but also for its clinical relevance because controlling the ability of mature CMs to replicate would provide a much-needed approach for restoring cardiac function in damaged hearts. In this review, we focus on the propensity of mature mammalian CMs to be multinucleated and polyploid, and the extent to which this may be necessary for normal physiology yet possibly disadvantageous in some circumstances. In this context, we explore whether the concept of the myonuclear domain (MND) in multinucleated skeletal muscle fibers might apply to cardiomyocytes, and whether cardio-MND size might be related to the transition of CMs to become multinuclear. Nuclei in CMs are almost certainly integrators of not only biochemical, but also-because of their central location within the myofibrils-mechanical information, and this multimodal, integrative function in adult CMs-involving molecules that have been extensively studied along with newly identified possibilities-could influence both gene expression as well as replication of the genome and the nuclei themselves.

KIF20A, highly expressed in immature hematopoietic cells, supports the growth of HL60 cell line

A microtubule-associated motor protein, kinesin-like family member 20A (KIF20A; also called MKlp2) is required for cytokinesis and contributes to intracellular vesicular trafficking. KIF20A plays a critical role in the development of several cancers, but its role in blood cells and hematological malignancies have not been studied. In the present study, we focused on the role of KIF20A in hematopoietic cells and possible involvement in myeloid neoplasms. We found that human leukemia cell lines and normal bone marrow CD34-positive cells stimulated by growth factors, but not mature peripheral blood cells, exhibit high KIF20A expression. We further found that HL60 cells, which originally express a large amount of KIF20A, showed decreased KIF20A expression in parallel with both neutrophil-like and macrophage-like differentiation-induction. KIF20A-knockdown using a lentivirus shRNA transfection system led to partial cell cycle arrest at the G2/M phase and frequent appearance of multinucleated cells. Treatment with a KIF20A-selective inhibitor, paprotrain enhanced the multinuclearity of KIF20A-knockdown cell clones and suppressed growth. The present study contributes to our understanding of the role of KIF20A in blood cells and leukemia cells in particular.