The cancer stem cell (CSC) hypothesis has captured the attention of many scientists. It is believed that elimination of CSCs could possibly eradicate the whole cancer. CSC surface markers provide molecular targeted therapies for various cancers, using therapeutic antibodies specific for the CSC surface markers. Various CSC surface markers have been identified and published. Interestingly, most of the markers used to identify CSCs are derived from surface markers present on human embryonic stem cells (hESCs) or adult stem cells. In this review, we classify the currently known 40 CSC surface markers into 3 different categories, in terms of their expression in hESCs, adult stem cells, and normal tissue cells. Approximately 73% of current CSC surface markers appear to be present on embryonic or adult stem cells, and they are rarely expressed on normal tissue cells. The remaining CSC surface markers are considerably expressed even in normal tissue cells, and some of them have been extensively validated as CSC surface markers by various research groups. We discuss the significance of the categorized CSC surface markers, and provide insight into why surface markers on hESCs are an attractive source to find novel surface markers on CSCs.

Recombinant Chinese hamster ovary (CHO) cells expressing a high‐level of chimeric antibody against S surface antigen of hepatitis B virus were obtained by co‐transfection of heavy and light chain cDNA expression vectors into dihydrofolate reductase (dhfr)‐deficient CHO cells and subsequent gene amplification in medium containing stepwise increments in methotrexate (MTX) level such as 0.02, 0.08, 0.32, 1.0, and 4.0 μM. The highest producer (HP) subclone was isolated from each MTX level and was characterized with respect to cell growth and antibody production in the corresponding level of MTX. The specific growth rate of the HP subclone was inversely proportional to the MTX level. On the other hand, its specific antibody productivity (qAb) rapidly increased with increasing MTX level up to 0.08 μM, and thereafter, it gradually increased to 20 μg/106 cells/day at 4 μM MTX. Southern blot analysis showed that the enhanced qAb at higher MTX level resulted from immunoglobulin (Ig) gene amplification. The stability of the HP subclones isolated at 0.02, 0.08, 0.32, and 1.0 μM MTX in regard to antibody production was investigated during long‐term culture in the absence of MTX. The qAb of all subclones significantly decreased during the culture. However, the relative extent of decrease in qAb was variable among the subclones. The HP subclone isolated at 1 μM MTX was most stable and could retain 59% of the initial qAb after 80 days of cultivation. Southern blot analysis showed that this decrease in qAb of the subclones resulted mainly from the loss of Ig gene copies during long‐term culture. Despite the decreased qAb, the HP subclone isolated at 1 μM MTX could maintain high volumetric antibody productivity over three months because of improved cell growth rate during long‐term culture. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:73–84, 1998.

Recombinant Chinese hamster ovary (CHO) cells expressing a high-level of chimeric antibody against S surface antigen of hepatitis B virus were obtained by co-transfection of heavy and light chain cDNA expression vectors into dihydrofolate reductase (dhfr)-deficient CHO cells and subsequent gene amplification in medium containing stepwise increments in methotrexate (MTX) level such as 0.02, 0.08, 0.32, 1.0, and 4.0 microM. The highest producer (HP) subclone was isolated from each MTX level and was characterized with respect to cell growth and antibody production in the corresponding level of MTX. The specific growth rate of the HP subclone was inversely proportional to the MTX level. On the other hand, its specific antibody productivity (qAb) rapidly increased with increasing MTX level up to 0.08 microM, and thereafter, it gradually increased to 20 microg/10(6) cells/day at 4 microM MTX. Southern blot analysis showed that the enhanced qAb at higher MTX level resulted from immunoglobulin (Ig) gene amplification. The stability of the HP subclones isolated at 0.02, 0.08, 0.32, and 1.0 microM MTX in regard to antibody production was investigated during long-term culture in the absence of MTX. The qAb of all subclones significantly decreased during the culture. However, the relative extent of decrease in qAb was variable among the subclones. The HP subclone isolated at 1 microM MTX was most stable and could retain 59% of the initial qAb after 80 days of cultivation. Southern blot analysis showed that this decrease in qAb of the subclones resulted mainly from the loss of Ig gene copies during long-term culture. Despite the decreased qAb, the HP subclone isolated at 1 microM MTX could maintain high volumetric antibody productivity over three months because of improved cell growth rate during long-term culture.

The proper folding and assembly of viral envelope proteins are mediated by host chaperones. In this study, we demonstrated that an endoplasmic reticulum luminal chaperone GRP78/BiP bound specifically to the pre-S1 domain of the L protein in vitro and in vivo where complete viral particles were secreted, suggesting that GRP78/BiP plays an essential role in the proper folding of the L protein and/or assembly of viral envelope proteins.The hepatitis B virus (HBV) is a noncytopathic doublestranded DNA virus of the hepadnavirus family that causes acute and chronic liver disease. Chronic HBV infection can lead to cirrhosis and finally to hepatocellular carcinoma. HBV is an enveloped virus whose envelope consists of three related proteins, designated the small (S), middle (M), and large (L) surface proteins (27). All of these proteins have a common carboxy-terminal sequence of 226 amino acid residues (S protein). The M protein has an additional sequence (pre-S2) of 55 amino acid residues located at the amino terminus. The L protein contains an additional sequence (pre-S1) of 108 or 119 amino acid residues (depending on the presence of subtype ay or ad, respectively) at the amino terminus of the M protein. All three proteins are found either unglycosylated or glycosylated at Asn146 of the S protein. The M protein is additionally glycosylated at Asn4 within its pre-S2 region (15). The M and S proteins are cotranslationally inserted into the endoplasmic reticulum (ER) membrane with their amino termini translocated in the ER lumen (9). Conversely, the pre-S region (pre-S1 plus pre-S2) of the L protein fails to be cotranslationally translocated and remains on the cytosolic side of the ER membrane. During maturation, approximately half of the L protein molecules posttranslationally translocate their pre-S region into the luminal space, thereby generating a dual topology that is maintained in the secreted viral particles (3,28,35). The dual transmembrane topology, disposing the pre-S region at either a luminal (external) or a cytosolic (internal) site, may provide such crucial functions as hepatocyte receptor binding or capsid envelopment, respectively, in the viral life cycle (3,28,35). The envelope proteins synthesized as transmembrane proteins of rough ER oligomerize rapidly. Virus assembly is thought to occur at post-ER/pre-Golgi membranes where preformed cytosolic nucleocapsids are packaged by transmembrane envelope proteins (2,18,40). Virions then bud into intraluminal cisternae and leave the cell via the constitutive pathway of secretion. An excess of M and S proteins, however, is not incorporated into virion envelopes but self-assembles into secreted subviral particles (15,26).Eucaryotic viruses usually use host cell factors during their entire life cycle. Given the known importance of cellular chaperones for correct folding and assembly of host proteins, it is likely that the proper folding and assembly of viral structural proteins are mediated by host chaperones. So far, two host chaperones are known to be involved ...

B-Cell receptor-associated protein 31 (BAP31) regulates the export of secreted membrane proteins from the endoplasmic reticulum (ER) to the downstream secretory pathway. Previously, we generated a monoclonal antibody 297-D4 against the surface molecule on undifferentiated human embryonic stem cells (hESCs). Here, we found that 297-D4 antigen was localized to pluripotent hESCs and downregulated during early differentiation of hESCs and identified that the antigen target of 297-D4 was BAP31 on the hESC-surface. To investigate the functional role of BAP31 in hESCs, BAP31 expression was knocked down by small interfering RNA. BAP31 depletion impaired hESC self-renewal and pluripotency and drove hESC differentiation into multicell lineages. BAP31 depletion hindered hESC proliferation by arresting cell cycle at G0/G1 phase and inducing caspase-independent cell death. Interestingly, BAP31 depletion reduced hESC adhesion to extracellular matrix (ECM). Analysis of cell surface molecules showed decreased expression of epithelial cell adhesion molecule (EpCAM) in BAP31-depleted hESCs, while ectopic expression of BAP31 elevated the expression of EpCAM. EpCAM depletion also reduced hESC adhesion to ECM, arrested cell cycle at G0/G1 phase and induced cell death, producing similar effects to those of BAP31 depletion. BAP31 and EpCAM were physically associated and colocalized at the ER and cell surface. Both BAP31 and EpCAM depletion decreased cyclin D1 and E expression and suppressed PI3K/Akt signaling, suggesting that BAP31 regulates hESC stemness and survival via control of EpCAM expression. These findings provide, for the first time, mechanistic insights into how BAP31 regulates hESC stemness and survival via control of EpCAM expression.