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Progranulin (PGRN) haploinsufficiency from autosomal dominant mutations in the PGRN gene causes frontotemporal lobar degeneration, which is characterized by cytoplasmic inclusions predominantly containing TDP-43 (FTLD-TDP). PGRN supplementation for patients with a PGRN gene mutation has recently been proposed as a therapeutic strategy to suppress FTLD-TDP. However, it currently remains unclear whether excessive amounts of PGRN are beneficial or harmful. We herein report the effects of PGRN overexpression on autophagic flux in a cultured cell model. PGRN overexpression increased the level of an autophagosome marker without promoting autophagosome formation and decreased the signal intensity of an autolysosome marker, indicating the suppression of autophagic flux due to reductions in the formation of autolysosomes. Assessments of lysosome numbers and biogenesis using LysoTracker and cells stably expressing TFEB-GFP, respectively, indicated that PGRN overexpression increased the lysosome numbers without lysosomal biogenesis. These results suggest that PGRN overexpression suppressed autophagic flux by inhibiting autophagosome-lysosome fusion. Moreover, PGRN overexpression enhanced polyglutamine aggregation and aggregate-prone TDP-43 accumulation, indicating that the suppression of autophagic flux by excessive amounts of PGRN worsens the pathology of neurodegenerative diseases., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Accurate DNA replication is at the heart of faithful genome transmission in dividing cells. DNA replication is strictly controlled by various factors. However, how environmental stresses such as nutrient starvation impact on these factors and DNA replication is largely unknown. Here we show that DNA replication is regulated by target of rapamycin complex 1 (TORC1) protein kinase, which is a central regulator of cell growth and proliferation in response to nutrients. TORC1 inactivation reduced the levels of various proteins critical for DNA replication initiation, such as Mcm3, Orc3, Cdt1, and Sld2, and retarded DNA replication. TORC1 inactivation promoted proteasome-mediated Mcm3 degradation. Skp1-Cullin-F-box (SCF)-Grr1 and PEST motif mediated Mcm3 degradation. TORC1-downstream factors PP2A-Cdc55 protein phosphatase and protein kinase A regulated Mcm3 degradation. This study showed that TORC1 signaling modulates DNA replication to coordinate cell growth and genome replication in response to nutrient availability., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Recent studies showed high frequencies of homoplasmic mtDNA mutations in various human tumor types, suggesting that the mutated mtDNA haplotypes somehow contribute to expression of tumor phenotypes. We directly addressed this issue by isolating mouse mtDNA-less (rho(0)) cells for complete mtDNA replacement between normal cells and their carcinogen-induced transformants, and examined the effect of the mtDNA replacement on expression of tumorigenicity, a phenotype forming tumors in nude mice. The results showed that genome chimera cells carrying nuclear DNA from tumor cells and mtDNA from normal cells expressed tumorigenicity, whereas those carrying nuclear DNA from normal cells and mtDNA from tumor cells did not. These observations provided direct evidence that nuclear DNA, but not mtDNA, is responsible for carcinogen-induced malignant transformation, although it remains possible that mtDNA mutations and resultant respiration defects may influence the degree of malignancy, such as invasive or metastatic properties.

We recently cloned a new leukemogenesis-associated gene MmTRA1a (Mm-1 cell derived transplantability-associated gene 1a, former name "TRA1") from a mouse leukemogenic and monocytic Mm-P cell cDNA library and also cloned its normal counterpart MmTRA1b (former name "NOR1") from a normal mouse kidney cDNA library. The mouse MmTRA1a is a truncated form of mouse MmTRA1b. Here we report the cloning of a cDNA (human MmTRA1b) homologous to the mouse MmTRA1b from a human monocytic U937 cell cDNA library. The human MmTRA1b cDNA predicts a peptide containing 318 amino acids with a calculated molecular weight of 35,047 Da. The predicted human MmTRA1b protein sequence shared 78% amino acid identity with the mouse counterpart (328 amino acids). Both the human homologue and mouse MmTRA1b protein but not MmTRA1a protein possess a proline-rich domain at the N-terminal end. The human MmTRA1b gene was mapped to chromosome 3q23. Expression of the human homologue was increased during differentiation of U937 cells induced by most typical differentiation inducers. Moreover, predicted amino acid sequence analysis of human MmTRA1b cDNA revealed perfect identity with the human plasma membrane phospholipid scramblase that is required for transbilayer movement of membrane phospholipids. These results provide new information on the possible roles of MmTRA1b/phospholipid scramblase and the truncated MmTRA1a in the leukemogenesis and differentiation of monocytic leukemia cells., (Copyright 1998 Academic Press.)

Protein factors playing a significant part in differentiation and development have been recently elucidated. However, low molecular factors which also seem to be essential remain still unknown, although only retinoic acid has become such a candidate. Cotylenins had been isolated as the plant-growth regulators, and have been found to affect a number of physiological processes of higher plants. Here we report that at the concentrations above 12.5 microg/ml (20 microM) cotylenin A induced the functional and morphological differentiation in murine (M1) and human myeloid leukemia (HL-60) cells. Although cotylenin A has some similarity to PMA both in carbotricyclic diterpene structure and in biological activity (i.e. differentiation-induction of HL-60 cells into macrophages), the activation of PKC and the elevation of Ca2+-levels by cotylenin A were not observed. Quite recently it has been reported that fusicoccin (closely related to cotylenin A)-targets are 14-3-3 proteins, which are at the crosspoint of a huge array of signalling and regulatory pathways. These results suggest that cotylenin A might become a useful tool for the elucidation of molecular mechanisms of differentiation and development.

2'-Deoxycoformycin (dCF), a specific and potent inhibitor of adenosine deaminase, has demonstrated significant antitumor effect on lymphoid malignancies. The drug induced functional and morphologic differentiation of myeloid leukemia cells in combination with 2'-deoxyadenosine (dAd), but not dCF alone. NB4, a cell line derived from a patient with t(15; 17) acute promyelocytic leukemia (APL) underwent granulocytic differentiation when treated with all-trans retinoic acid (ATRA) or dCF plus dAd, but not with cytosine arabinoside. Pre-exposure of NB4 cells to ATRA greatly potentiated differentiation induced by dCF plus dAd, but pretreatment with dCF plus dAd before exposure to ATRA was less effective. Differentiation of NB4 cells was effectively induced by clinically applicable concentrations of dCF in combination with dAd. These findings may provide useful information about induction of differentiation in vivo.

Mouse myeloid leukemic line M1 cells can be induced to differentiate into the monocyte/macrophage pathway by various inducers. The induction of differentiation of M1 cells can be inhibited by protein inhibitors termed differentiation inhibiting factors (I-factors) in a cell lysate and conditioned medium of differentiation resistant M1 cells. Production of the I-factor activity in resistant M1 cells is well associated with development of resistance of M1 cells to differentiation inducers. We have now purified one of the I-factors from conditioned medium of differentiation resistant M1 cells. The purified I-factor has a relative molecular mass of approximately 16000-17000 Da (16K I-factor). The amino acid sequence of all fragments of the 16K I-factor we have found are identical with Nm23/nucleoside diphosphate kinase (EC2.7.4.6) protein involved in tumor metastasis. The findings indicate that the I-factor, a candidate suppressor protein for differentiation of leukemic cells, is Nm23/nucleoside diphosphate kinase protein.