Variant Forms of α-Fetoprotein Transcripts Expressed in Human Hematopoietic Progenitors

Abstract

Hematopoietic stem cells have been identified as multipotent cells that give rise to all adult hematopoietic lineages. Although the hematopoietic lineage is derived from the mesodermal germ layer in the embryo, recent data suggest that bone marrow cells with an antigenic profile consistent with that of hematopoietic stem cells can also differentiate to cell types of the endodermal lineages, such as hepatocytes. However, the molecular mechanisms associated with these events are entirely unknown. For decades, ␣-fetoprotein (AFP) has been used as a differentiation marker for endodermal cells, because it was thought that the transcription of AFP mRNA is tightly regulated in a developmental and tissue-specific process. In this report we describe two new variant forms of AFP transcripts in human hematopoietic progenitors that are not expressed in mature cells. The variant AFP (vAFP) cDNA sequences isolated from a multipotent hematopoietic cell line, K562, revealed that the vAFP differed from the authentic transcript, consisting of 15 exons, by replacing exon 1 of AFP with one or two exons located in the 5-untranslated region of the AFP gene. In addition to the K562 cell line, vAFP transcripts were detected in normal bone marrow, thymus, and brain but were not detected in normal spleen, intestine, liver, or the hepatocellular carcinoma cell line, HepG2. This suggests expression in normal hematopoietic progenitors. This hypothesis was confirmed by the finding that CD34 ؉ Lin ؊ hematopoietic progenitor cells purified from cord blood by flow cytometric sorting also expressed the variant transcripts. These results suggest that some hematopoietic progenitors are in a state that permits them to express certain types of transcripts that have been considered unique to endoderm.

Human Cord Blood Stem Cells Generate Human Cytokeratin 18-Negative Hepatocyte-Like Cells in Injured Mouse Liver

“…Second, transplantation of cells into mice with a NOD-SCID immunodeficient background may facilitate the differentiation of stem cells into hepatocytes and third, neonatal hUCB cells may have a reservoir of preformed hepatic progenitors, which may not be present in mouse BM preparations. 25,26 In our experiments we did not find evidence that the NOD-SCID immunodeficient background of the recipient animals facilitated the in vivo differentiation of murine hematopoietic stem cells into hepatocytes. We used EGFP transgenic murine hematopoietic cells for the transplantation study to unequivocally detect BM-derived cells in the liver.…”

“…24 One study has shown expression of a variant AFP transcript in hUCB cells that might suggest the presence of some nonhematopoietic primitive progenitors that might have the potential to differentiate into cells of hepatic as well as hematopoietic phenotype. 25,26 hUCB is highly enriched for hematopoietic stem cells and can partially repopulate the BM of NOD-SCID mice. A few recent articles have highlighted the differentiation potential of human cord blood cells and the generation of human hepatocytes from transplanted cord blood cells in NOD-SCID mice.…”

Mapping of Structure-Function Peptide Sites on the Human Alpha-fetoprotein Amino Acid Sequence

“…Furthermore, truncated forms of HAFP (~50 kDa) have been detected in cell cultures comprised of hepatomas, testicular embryonal carcinomas, and breast tumors (Mizejewski, 2002). Variant forms of HAFP transcripts from non-translated regions of the AFP mRNA have recently been reported in CD34+ hematopoietic progenitor cells derived from mesodermal germ cells (Kubota et al, 2002). These latter investigators described two variant forms of HAFP mRNA that were not expressed in mature adult cells.…”

Future of cord blood for non-oncology uses

“…In vitro by RT-PCR, alizarin red and von Kossa-staining, ALP detection, immunohistochemistry and western blot 8,31,[110][111][112][113] In vitro by safranin-O staining, RT-PCR and immunohistochemistry 8,31 In vitro by immunohistochemistry, RT-PCR, calcium imaging and western blot [114][115][116][117] In vivo in parkinsonian rat model, ischemic rat model [118][119][120][121][122][123] In vitro by immunohistochemistry, RT-PCR, PAS-staining, urea and albumin production, western blot and LDL uptake 31,94,124,125 CD34/AC133-positive (hematopoietic progenitor) cells In vitro by RT-PCR 126 In vivo in NOD/SCID mouse model 95,96 Not defined cells from MNC In vitro by immunohistochemistry, whole-cell patch-clamp, western blot and RT-PCR [127][128][129][130][131] In vivo in spinal cord injury and intra-brain injection in rat and NOD/SCID mouse model 73,76,[80][81][82][83][84][86][87][88][89][90][91][92]<...>…”