Effects of Simulated Microgravity on Embryonic Stem Cells

There have been many studies on the biological effects of simulated microgravity (SMG) on differentiated cells or adult stem cells. However, there has been no systematic study on the effects of SMG on embryonic stem (ES) cells. In this study, we investigated various effects (including cell proliferation, cell cycle distribution, cell differentiation, cell adhesion, apoptosis, genomic integrity and DNA damage repair) of SMG on mouse embryonic stem (mES) cells. Mouse ES cells cultured under SMG condition had a significantly reduced total cell number compared with cells cultured under 1 g gravity (1G) condition. However, there was no significant difference in cell cycle distribution between SMG and 1G culture conditions, indicating that cell proliferation was not impaired significantly by SMG and was not a major factor contributing to the total cell number reduction. In contrast, a lower adhesion rate cultured under SMG condition contributed to the lower cell number in SMG. Our results also revealed that SMG alone could not induce DNA damage in mES cells while it could affect the repair of radiation-induced DNA lesions of mES cells. Taken together, mES cells were sensitive to SMG and the major alterations in cellular events were cell number expansion, adhesion rate decrease, increased apoptosis and delayed DNA repair progression, which are distinct from the responses of other types of cells to SMG

Two Estrogen Response Element Sequences Near the PCNA Gene Are Not Responsible for Its Estrogen-Enhanced Expression in MCF7 Cells

The proliferating cell nuclear antigen (PCNA) is an essential component of DNA replication, cell cycle regulation, and epigenetic inheritance. High expression of PCNA is associated with poor prognosis in patients with breast cancer. The 5'-region of the PCNA gene contains two computationally-detected estrogen response element (ERE) sequences, one of which is evolutionarily conserved. Both of these sequences are of undocumented cis-regulatory function. We recently demonstrated that estradiol (E2) enhances PCNA mRNA expression in MCF7 breast cancer cells. MCF7 cells proliferate in response to E2.Here, we demonstrate that E2 rapidly enhanced PCNA mRNA and protein expression in a process that requires ERalpha as well as de novo protein synthesis. One of the two upstream ERE sequences was specifically bound by ERalpha-containing protein complexes, in vitro, in gel shift analysis. Yet, each ERE sequence, when cloned as a single copy, or when engineered as two tandem copies of the ERE-containing sequence, was not capable of activating a luciferase reporter construct in response to E2. In MCF7 cells, neither ERE-containing genomic region demonstrated E2-dependent recruitment of ERalpha by sensitive ChIP-PCR assays.We conclude that E2 enhances PCNA gene expression by an indirect process and that computational detection of EREs, even when evolutionarily conserved and when near E2-responsive genes, requires biochemical validation

PCNA levels in neuroblastoma are increased in tumors with an amplified N- myc gene and in metastatic stage tumors

N- myc oncogene amplification in neuroblastoma has been found to be significantly associated with advanced stage disease and tumor progression. However, there is a lack of data on tumors, regarding the relationship between N- myc gene amplification and proliferation activity. Proliferating cell nuclear antigen (PCNA) is a proliferation-induced 36 kD nuclear protein that is the auxiliary component of DNA polymerase δ. PCNA levels in tissues have been found to correlate with proliferative activity. We have examined PCNA levels in neuroblastomas in relation to N- myc gene amplification and tumor stage. Statistically, significantly higher levels of PCNA were observed in tumors with an amplified N- myc gene relative to tumors with a single gene copy. The highest levels of PCNA were observed in advanced stage tumors with an amplified N- myc gene. Treatment of neuroblastoma cells in culture with retinoic acid, which induces differentiation, resulted in a substantial decrease in PCNA. Our results suggest that PCNA levels may reflect differences in proliferative activity between neuroblastomas, related to stage of the disease and to N- myc gene copy number.[/p ]Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42581/1/10585_2004_Article_BF00880069.pd