Mitofusins and Drp1 are key components in mitochondrial membrane fusion and division, but the molecular mechanism underlying the regulation of their activities remains to be clarified. Here, we identified human membrane-associated RING-CH (MARCH)-V as a novel transmembrane protein of the mitochondrial outer membrane. Immunoprecipitation studies demonstrated that MARCH-V interacts with mitofusin 2 (MFN2) and ubiquitinated forms of Drp1. Overexpression of MARCH-V promoted the formation of long tubular mitochondria in a manner that depends on MFN2 activity. By contrast, mutations in the RING finger caused fragmentation of mitochondria. We also show that MARCH-V promotes ubiquitination of Drp1. These results indicate that MARCH-V has a crucial role in the control of mitochondrial morphology by regulating MFN2 and Drp1 activities.

The proto-oncogene product pp60 c-src is the cellular homologue of the Rous sarcoma transforming gene, and it is a non-receptor-linked and membrane-associated tyrosine kinase. There is a close correlation between elevated pp60 c-src activity and cell transformation. We have recently reported that pp60 c-src was activated in hepatocellular carcinoma (HCC) of human and Long-Evans cinnamon (LEC) rats. However, the mechanisms involved in this process remain unknown. C-terminal Src kinase (Csk) is a novel cytoplasmic protein tyrosine kinase that inactivates the members of the Src family protein tyrosine kinase in vitro. A large number of cellular protein tyrosine kinase (PTK) genes have been cloned and sequenced. These kinases are classified into two major groups: the first comprises growth factor receptor tyrosine kinases; the second includes retroviral protein PTKs and their cellular homologues. 1 The main representatives of the latter group are non-receptor-linked and membrane-associated src-related tyrosine kinases. 2 At least nine src-related tyrosine kinases have been identified. We investigated the role of Csk in hepatocarcinogenesis by

In a previous investigation, a 35 kDa iron-regulated protein was identified from total cellular proteins of Pasfeurella haemolytica grown under irondepleted conditions. This study reports identification of the gene (fbpA) encoding the 35 kDa protein based on complementation of an entA Escherichia coli strain transformed with a plasmid derived from a P. haemolytica lambda ZAP II library. Cross-reactivity was demonstrated between an anti-35 kDa mAb and a 35 kDa protein expressed in this strain. Furthermore, a translated ORF identified on the recombinant plasmid corresponded with the N-terminal amino acid sequence of the intact and a CNBr-cleaved fragment of the 35 kDa iron-regulated protein. Nucleotide sequence analysis of the gene encoding the 35 kDa protein demonstrated homology with the cluster 1 group of extracellular solute-binding proteins, especially to the iron-binding proteins of this family. Complete sequence analysis of the recombinant plasmid insert identified three other predominant ORFs, two of which appeared to be in an operonic organization with fbpA. These latter components (fbpB and fbpC) showed homology to the transmembrane and ATPase components of ATPbinding cassette (ABC)-type uptake systems, respectively. Based on amino acicUDNA sequencing, citrate competition assay of iron affinity and visible wavelength spectra, it was concluded that the P. haemolytica 35 kDa protein functions as an FbpA homologue (referred to as PFbpA) and that the gene encoding this protein is part of an operon comprising a member of the FbpABC family of iron uptake systems. Primary sequence analysis revealed rather surprisingly that PFbpA is more closely related to the intracellular Mn/Febinding protein ldiA found in cyanobacteria than to any of the homologous FbpA proteins currently known in commensal or pathogenic members of the Past eurellaceae or Neisseriaceae .~~

and chromobindins. 15 AXs were first described as glucocortiAnnexin (AX) constitutes a new family of Ca 2/ -depencoid-inducible inhibitory proteins of phospholipase A 2 . 13,14 dent membrane-binding proteins; 13 of them have been These proteins possess four or eight conserved 70 amino acid described. Among these, annexin-I (AX-I) has displayed repeats, which comprise the core domain, where Ca 2/ -and many biological functions in vitro. Its actual role in vivo, phospholipid-binding functions are located. Annexins have however, remains unknown. We already reported that unique N-terminal tails that vary in length and sequence. 3,15 AX-I was expressed in proliferating (regenerating) hepaSubsequent studies have shown that AX-I (molecular weight, tocytes at both protein and messenger RNA (mRNA) lev-35 kd) is identical to the Ca 2/ -dependent phospholipid-and els. The role of AX-I in human hepatocellular carcinoma actin-binding protein. 2,16,17 In particular, AX-I is the major (HCC) remains obscure. In this study, the amounts of substrate for epidermal growth factor receptor (EGFR) ki-AX-I at protein and mRNA levels, as well as its localizanase, [17][18][19][20][21][22][23] and also for serine/threonine kinases such as protion, have been determined in the normal human liver, tein kinase C. 24 Various AXs have been implicated in cellular chronic hepatitis liver, and nontumorous and tumorous processes, including modulation of phospholipase A 2 activity portions of HCC. AX-I was rarely found in normal and and inflammation, 13,14,25 exocytosis, 26-28 differentiation, 29,30 chronic liver tissues, whereas it is overexpressed at both proliferation, 31-33 blood coagulation, 34 immune response, 35 the transcriptional and translational levels in tumorous membrane-cytoskeletal linkage, 36 and intracellular signal and nontumorous regions of HCC. In addition, more AXtransduction. 37,38 Although the conservation of AXs during I was expressed in the tumorous portion than the nontuevolution argues strongly for their important physiological morous portion of HCC. AX-I was present in the hepatoroles, this notion remains confusing and controversial. cytes and HCC cells, localized mainly in the cytoplasm.The in vivo phosphorylation of AX-I is induced by stimula-AX-I was overexpressed in poorly differentiated cancer tion with EGFR, and it profoundly affects its Ca 2/ requirecells. Furthermore, AX-I was tyrosine-phosphorylated in ment for phospholipid binding. [18][19][20][21]23 Although these results HCC. We also found that some of the AX-I-positive hepaare consistent with the roles of AX-I in cell transformation tocytes in the nontumorous tissues were derived from a and stimulation of cell growth, 32 such roles have yet to be particular subset of parenchymal cells (stem or oval delineated. We earlier showed that AX-I levels increase in cells). These results indicate that AX-I plays an improliferative (or regenerative) hepatocytes, suggesting that portant role in the malignant transformation process it plays a specific role in this event....

No abstract