Biomedical subjects

Richard L Riley

Publications and source records attributed to Richard L Riley.

5 recordsLinked to original sources

PubMed2003

The age-related decrease in E47 DNA-binding does not depend on increased Id inhibitory proteins in bone marrow-derived B cell precursors.

Our previous results showed that decreased numbers of pre-B cells in aged mice were associated with decreases in surrogate light chain, lambda5, and transcription factors E47/E12. In the present paper, we have analyzed IL-7-expanded populations of pro-B/early pre-B cells to evaluate whether the age-related reduction in E47 DNA-binding could be attributed to reduced E47 expression and/or increased Id expression. According to the percentage of pre-B cells present in their bone marrow, old mice were classified as severely depleted (>80% loss in pre-B cells, 50% loss in pro-B cells), or moderately depleted (20-80% loss in pre-B cells). Results herein show that IL-7-stimulated pro-B/pre-B cells from both severely depleted and moderately depleted old mice exhibit a reduced E47 DNA-binding capacity compared to young mice, and this defect in severely depleted old mice is more dramatic than that in moderately depleted old mice. Id proteins, which are inhibitors of E47, are not increased in nuclear extracts of IL-7-expanded pro-B/early pre-B cells from severely depleted or moderately depleted old mice. We therefore conclude that the reduced expression of E47 protein alone in severely depleted and to a lesser extent in moderately depleted old mice explains the reduced amount of E47-DNA binding.

Age Factors↗

PubMed2003

Decreased E12 and/or E47 transcription factor activity in the bone marrow as well as in the spleen of aged mice.

The E2A-encoded transcription factors E12 and E47 are key regulators of B cell functions. They bind to the E-box site, found in regulatory regions of B cell-specific genes; promote cell survival of early pre-B cells; help to initiate Ig rearrangements; and are also involved in class switch in mature B cells in the periphery. We have investigated the expression and function of E47 and E12 in IL-7-expanded pro-B/pre-B cell precursors and in unstimulated or LPS-activated splenic B cells from young and old BALB/c mice. Results show that B cell precursors from the bone marrow of old mice exhibit a reduced expression of E2A proteins and a reduced ability to bind DNA, as compared with young mice. In the spleen, E2A protein expression and DNA binding are present in unstimulated B cells from young mice and, to a significantly lesser extent, from old mice. These are both strongly induced by activation in splenic B cells from young mice but only moderately induced in old mice, indicating that aging affects the expression and activity of E2A-encoded genes and also that DNA binding correlates with the amount of protein expression. The levels of E2A DNA binding in the spleen correlate with those in the bone marrow for individual mice. In splenic mature B cells, only E47/E47 complexes bind DNA; whereas in bone marrow B cell precursors, E47/E12 complexes participate in DNA binding. Only nuclear extracts of splenic mature B cells, but both nuclear and cytoplasmic extracts of bone marrow B cell precursors, exhibit DNA binding.

Aging↗

PubMed2003

B cell precursors in senescent mice exhibit decreased recruitment into proliferative compartments and altered expression of Bcl-2 family members.

In vitro, aged pro-B cells generally exhibit limited expansion in response to IL-7 when compared to young pro-B cells. CFSE-labeling in vitro indicated that aged mice have a lower frequency of pro-B cells which are capable of undergoing extensive proliferation upon stimulation with exogenous IL-7. Protein levels of the survival molecule Bcl-x(L) were consistently reduced in IL-7 expanded aged pro-B cells. Levels of both Bcl-2 and Baxalpha proteins were variable in aged B cell precursors. The expansion of aged pro-B cells in response to IL-7 in vitro correlated inversely with the ratio of the pro-apoptotic protein Baxalpha to the survival protein Bcl-2. Expansion of aged pro-B cells in vitro is likely dictated by both recruitment of pro-B cells into proliferative compartments and their survival; in aged B cell precursors, the latter is favored by low Baxalpha to Bcl-2 protein ratios.

Animals↗

PubMed2003

Effects of aging on proliferation and E47 transcription factor activity induced by different stimuli in murine splenic B cells.

In the present paper, we have investigated the effects of aging on the expression and function of the E2A-encoded transcription factor E47 in splenic B lymphocytes, unactivated or activated with different stimuli (LPS, anti-CD40, anti-IgM, alone or in combination with IL-4). Results indicate that unstimulated splenic B cells show very low E47 protein levels as well as E47 DNA-binding activity and that, upon B cell activation, E47 expression and DNA-binding activity are strongly induced in young and, to a significantly lesser extent, in old mice. The level of E47 protein expression in stimulated splenic B cells was found significantly higher in young than in old mice, suggesting that DNA-binding activity correlates with protein expression. These results altogether suggest that the reduced expression of the transcriptional regulator E47 could help explain the reduced B cell functions in aging mice.

Aging↗

PubMed2002

Levels of E2A protein expression in B cell precursors are stage-dependent and inhibited by stem cell factor (c-kit ligand).

OBJECTIVE: The E2A-encoded proteins E47 and E12 are crucial to the development of pro-B and pre-B cells. The expression of E2A protein and mRNA during early B lymphopoiesis was determined and effects of stem cell factor (SCF; Steel factor; c-kit ligand) on E2A expression were evaluated. MATERIALS AND METHODS: Ex vivo murine pro-B cells and pre-B cells were isolated and in vitro B cell precursors were derived after culture of bone marrow with rmIL-7. Levels of E2A proteins were determined by Western analysis and mRNA by RT-PCR. E2A expression in vitro was also assessed in cultures supplemented with IL-7 +/- recombinant murine SCF (rmSCF), insulin-like growth factor-1 (rhIGF-1), or Flt3-ligand (rhFlt3-L). Turnover of E2A proteins was assessed following cycloheximide treatment. RESULTS: Ex vivo, pro-B cells had lower E47 protein levels than did pre-B cells but had comparable E2A mRNA levels. E2A protein, but not mRNA, levels were reduced in pro-B cells upon culture in vitro with IL-7 + rmSCF. This was associated with increased turnover of E2A proteins. In contrast, culture with IL-7 + IGF-1 or Flt3-L had minimal effects on E2A protein levels. CONCLUSION: Pre-B cells expressed higher levels of E2A protein than did pro-B cells and this mainly resulted from posttranscriptional regulation. Exogenous SCF inhibited E2A protein, but not mRNA, expression in cultured B cell precursors, possibly by increasing E2A protein turnover. The capacity to respond to SCF may influence the levels of E2A during B-cell development.

Animals↗