Cardiomyocyte--specific expression of the nuclear matrix protein, CIZ1, stimulates production of mono-nucleated cells with an extended window of proliferation in the postnatal mouse heart

Akt1 and dCIZ1 promote cell survival from apoptotic caspase activation during regeneration and oncogenic overgrowth

Apoptosis is an ancient and evolutionarily conserved cell suicide program. During apoptosis, executioner caspase enzyme activation has been considered a point of no return. However, emerging evidence suggests that some cells can survive caspase activation following exposure to apoptosis-inducing stresses, raising questions as to the physiological significance and underlying molecular mechanisms of this unexpected phenomenon. Here, we show that, following severe tissue injury, Drosophila wing disc cells that survive executioner caspase activation contribute to tissue regeneration. Through RNAi screening, we identify akt1 and a previously uncharacterized Drosophila gene CG8108, which is homologous to the human gene CIZ1, as essential for survival from the executioner caspase activation. We also show that cells expressing activated oncogenes experience apoptotic caspase activation, and that Akt1 and dCIZ1 are required for their survival and overgrowth. Thus, survival following executioner caspase activation is a normal tissue repair mechanism usurped to promote oncogene-driven overgrowth.

DNA damage and neurodegenerative phenotypes in aged Ciz1 null mice

Cell-cycle dysfunction and faulty DNA repair are closely intertwined pathobiological processes that may contribute to several neurodegenerative disorders. CDKN1A interacting zinc finger protein 1 (CIZ1) plays a critical role in DNA replication and cell-cycle progression at the G1/S checkpoint. Germline or somatic variants in CIZ1 have been linked to several neural and extra-neural diseases. Recently, we showed that germline knockout of Ciz1 is associated with motor and hematological abnormalities in young adult mice. However, the effects of CIZ1 deficiency in much older mice may be more relevant to understanding age-related declines in cognitive and motor functioning and age-related neurologic disorders such as isolated dystonia and Alzheimer disease. Mouse embryonic fibroblasts from Ciz1^-/- mice showed abnormal sensitivity to the effects of γ-irradiation with persistent DNA breaks, aberrant cell-cycle progression, and apoptosis. Aged (18-month-old) Ciz1^-/- mice exhibited marked deficits in motor and cognitive functioning, and, in brain tissues, overt DNA damage, NF-κB upregulation, oxidative stress, vascular dysfunction, inflammation, and cell death. These findings indicate that the deleterious effects of CIZ1 deficiency become more pronounced with aging and suggest that defects of cell-cycle control and associated DNA repair pathways in postmitotic neurons could contribute to global neurologic decline in elderly human populations. Accordingly, the G1/S cell-cycle checkpoint and associated DNA repair pathways may be targets for the prevention and treatment of age-related neurodegenerative processes.