Microchimerism in renal allografts: clinicopathological associations according to the type of chimeric cells.

AIMS: Recent studies have highlighted the presence of microchimerism in various solid allografts. The biological significance of these chimeric cells is controversial. They may be beneficial, leading to better tolerance of grafts or participating in tissue repair or, in contrast, deleterious if involved in chronic lesions. The aim was to assess the frequency and cellular nature of microchimerism in female renal grafts of male recipients by combined fluorescence in situ hybridization (FISH) for Y chromosome and immunohistochemistry and to investigate associations between intragraft microchimerism and histological lesions or allograft outcome. METHODS AND RESULTS: We screened 33 renal biopsy specimens, including 11 with acute T-cell-mediated rejection and nine with transplant glomerulopathy, from 22 male recipients transplanted with female kidneys by FISH and immunohistochemistry with antibodies against smooth muscle actin (mesangial cells), CD31 (endothelial cells), KL1 (epithelial cells), CD45 (leucocyte common antigen) and glomerular epithelial protein 1 (podocytes). Tubular microchimerism was detected in 71% of the patients with a mean percentage of chimeric epithelial cells of 1.4%. Glomerular microchimerism involving podocytes, mesangial and endothelial cells was present with a mean number of chimeric cells per glomerular section of, respectively, 0.6, 2.66 and 3.53. There was an association between endothelial microchimerism and a previous episode of acute T-cell-mediated rejection. CONCLUSIONS: In conclusion, microchimerism in renal grafts occurs frequently, but at a low level and affects tubular cells and all glomerular cell compartments in human renal allografts.

Internal radiotherapy of liver cancer with rat hepatocarcinoma-intestine-pancreas gene as a liver tumor-specific promoter.

The hepatocarcinoma-intestine-pancreas (HIP) gene, also called pancreatitis-associated protein-1 (PAP1) or Reg IIIalpha, is activated in most human hepatocellular carcinomas (HCCs) but not in normal liver, which suggests that HIP regulatory sequence could be used as efficient liver tumor-specific promoters to express a therapeutic polynucleotide in liver cancer. The sodium iodide symporter (NIS), which has recognized therapeutic and reporter gene properties, is appropriate to evaluate the transcriptional strength and specificity of the HIP promoter in HCC. For this purpose, we constructed a recombinant rat HIP-NIS adenoviral vector (AdrHIP-NIS), and evaluated its performance as a mediator of selective radioiodide uptake in tumor hepatocytes. Western blot, immunofluorescence, and iodide uptake assays were performed in AdrHIP-NIS-infected primary hepatocytes and transformed hepatic and nonhepatic cells. Nuclear imaging, tissue counting and immunohistochemistry were performed in normal and HCC-bearing Wistar rats infected with AdrHIP-NIS intratumorally or via the hepatic artery. In AdrHIP-NIS-infected transformed hepatic cells, functional NIS was strongly expressed, as in cells infected with a cytomegalovirus-NIS vector. No NIS expression was found in AdrHIP-NIS-infected normal hepatocytes or transformed nonhepatic cells. In rats bearing multinodular HCC, AdrHIP-NIS triggered functional NIS expression that was preferential in tumor hepatocytes. Administration of 18 mCi of (131)I resulted in the destruction of AdrHIP-NIS-injected nodules. This study has identified the rHIP regulatory sequence as a potent liver tumor-specific promoter for the transfer of therapeutic genes, and AdrHIP-NIS-mediated (131)I therapy as a valuable option for the treatment of multinodular HCC.

Liver tetraploidization is controlled by a new process of incomplete cytokinesis.

Cytokinesis is precisely controlled in both time and space to ensure equal distribution of the genetic material between daughter cells. Incomplete cytokinesis can be associated with developmental or pathological cell division programs leading to tetraploid progenies. In this study we decipher a new mechanism of incomplete cytokinesis taking place in hepatocytes during post-natal liver growth. This process is initiated in vivo after weaning and is associated with an absence of anaphase cell elongation. In this process, formation of a functional contractile actomyosin ring was never observed; indeed, actin filaments spread out along the cortex were not concentrated to the putative site of furrowing. Recruitment of myosin II to the cortex, controlled by Rho-kinase, was impaired. Astral microtubules failed to contact the equatorial cortex and to deliver their molecular signal, preventing activation of the RhoA pathway. These findings reveal a new developmental cell division program in the liver that prevents cleavage-plane specification.

The intraflagellar transport component IFT88/polaris is a centrosomal protein regulating G1-S transition in non-ciliated cells.

Loss of normal primary cilia function in mammals is linked to proliferative diseases, such as polycystic kidney disease, suggesting a regulatory relationship between cilia and cell cycle. The primary cilium expressed by most mammalian cells is nucleated from the elder centriole of the centrosome. The relationship between centrosome and cilia suggests that these structures share functions and components. We now show that IFT88/polaris, a component of the intraflagellar transport, remains associated to the centrosome in a proliferative state. IFT88/polaris is tightly associated with the centrosome throughout the cell cycle in a microtubule- and dynein-independent manner. IFT88/polaris tetratricopeptide repeat motifs are essential for this localization. Overexpression of IFT88/polaris prevents G1-S transition and induces apoptotic cell death. By contrast, IFT88/polaris depletion induced by RNA interference promotes cell-cycle progression to S, G2, and M phases. Finally, we demonstrate that IFT88/polaris interacts with Che-1, an Rb-binding protein that inhibits the Rb growth suppressing function. We propose that IFT88/polaris, a protein essential for ciliogenesis, is also crucial for G1-S transition in non-ciliated cells.

Conserved balance of hepatocyte nuclear DNA content in mononuclear and binuclear hepatocyte populations during the course of chronic viral hepatitis.

AIM: To analyze the percentages of hepatocytes with increased nuclear DNA content, i.e., tetraploid (4n) and octoploid (8n) nuclei, and then compared mononuclear and binuclear hepatocyte populations. METHODS: The percentages of mononuclear diploid (2n), 4n, and 8n hepatocytes and those of binuclear 2 x 2n, 2 x 4n, and 2 x 8n hepatocytes were determined with a method that can simultaneously measure hepatocyte nuclear DNA content and binuclearity in 62 patients with chronic hepatitis B or C. The percentage of 4n and 8n hepatocytes in the mononuclear hepatocyte population was compared with the percentage of 2 x 4n and 2 x 8n hepatocytes in the binuclear hepatocyte population. RESULTS: The percentages of 4n and 8n hepatocytes in mononuclear hepatocytes and 2 x 4n and 2 x 8n hepatocytes in binuclear hepatocytes were similar, regardless of the activity or fibrosis grade of chronic hepatitis and regardless of the infecting virus. CONCLUSION: The distribution of nuclear DNA content within mononuclear and binuclear hepatocyte populations was conserved during the course of chronic viral hepatitis.

Liver cell polyploidization: a pivotal role for binuclear hepatocytes.

Polyploidy is a general physiological process indicative of terminal differentiation. During liver growth, this process generates the appearance of tetraploid (4n) and octoploid (8n) hepatocytes with one or two nuclei. The onset of polyploidy in the liver has been recognized for quite some time; however, the cellular mechanisms that govern it remain unknown. In this report, we observed the sequential appearance during liver growth of binuclear diploid (2 x 2n) and mononuclear 4n hepatocytes from a diploid hepatocyte population. To identify the cell cycle modifications involved in hepatocyte polyploidization, mitosis was then monitored in primary cultures of rat hepatocytes. Twenty percent of mononuclear 2n hepatocytes failed to undergo cytokinesis with no observable contractile movement of the ring. This process led to the formation of binuclear 2 x 2n hepatocytes. This tetraploid condition following cleavage failure did not activate the p53-dependent checkpoint in G1. In fact, binuclear hepatocytes were able to proceed through S phase, and the formation of a bipolar spindle during mitosis constituted the key step leading to the genesis of two mononuclear 4n hepatocytes. Finally, we studied the duplication and clustering of centrosomes in the binuclear hepatocyte. These cells exhibited two centrosomes in G1 that were duplicated during S phase and then clustered by pairs at opposite poles of the cell during metaphase. This event led only to mononuclear 4n progeny and maintained the tetraploidy status of hepatocytes.