Impaired bone marrow microenvironment and immune function in T cell protein tyrosine phosphatase-deficient mice.

The T cell protein tyrosine phosphatase (TC-PTP) is one of the most abundant mammalian tyrosine phosphatases in hematopoietic cells; however, its role in hematopoietic cell function remains unknown. In this report, we investigated the physiological function(s) of TC-PTP by generating TC-PTP-deficient mutant mice. The three genotypes (+/+, +/-, -/-) showed mendelian segregation at birth (1:2:1) demonstrating that the absence of TC-PTP was not lethal in utero, but all homozygous mutant mice died by 3-5 wk of age, displaying runting, splenomegaly, and lymphadenopathy. Homozygous mice exhibited specific defects in bone marrow (BM), B cell lymphopoiesis, and erythropoiesis, as well as impaired T and B cell functions. However, myeloid and macrophage development in the BM and T cell development in the thymus were not significantly affected. BM transplantation experiments showed that hematopoietic failure in TC-PTP -/- animals was not due to a stem cell defect, but rather to a stromal cell deficiency. This study demonstrates that TC-PTP plays a significant role in both hematopoiesis and immune function.

Thermosensitive mutants of the MPTP and hPTP1B protein tyrosine phosphatases: isolation and structural analysis.

A PCR-based random mutagenesis procedure was employed to identify several thermosensitive mutants of the MPTP enzyme, the murine homologue of the human T-cell PTPase and rat PTP-S enzymes. Four mutants with varying degrees of thermosensitivity were characterized for their thermostability and refolding properties following incubation at the nonpermissive temperature. Structure analysis of these mutations based on the hPTP1B co-ordinate structure demonstrates a clear relationship between the position of each mutated amino acid relative to the catalytic cysteine residue and their thermostability. Introduction of two of these mutations in the related enzyme hPTP1B suggests that the structural defects and the resulting thermosensitivity of these mutations may represent an intrinsic property of all PTPase catalytic domains.

Promoter analysis of the murine T-cell protein tyrosine phosphatase gene.

The T-cell protein tyrosine phosphatase (TC PTP) is expressed ubiquitously at all stages of mammalian development. However, mRNA levels fluctuate in a cell-cycle-dependent manner, reaching peak levels in late G1, and rapidly decreasing in S phase. Furthermore, TC PTP being present in higher amounts in lymphoid tissues, we have recently shown that it is essential for proper maintenance of both the bone marrow micro-environment and B- and T-cell functions. In order to better understand the elements controlling the expression pattern of this gene, we have isolated and characterized approx. 4kb of the murine TC PTP promoter. DNA sequencing of the proximal 5' region revealed the absence of both TATAA and CAAT boxes. Primer extension analysis and S1 nuclease mapping techniques identified multiple transcription initiation sites. Functional promoter activity was determined using transfection experiments of promoter deletion constructs fused to a CAT reporter construct. Our results indicate that the minimal promoter sequence required for functional expression is contained within the first 147bp of the TC PTP promoter. In addition, consistent with the cell-cycle-dependent expression of TC PTP, we localized a domain between 492 and 1976bp from the transcription initiation site through which repression occurs. In conclusion, although initiator-driven transcription allows for ubiquitous expression of TC PTP, we define general transcription motifs present within the promoter that may mediate specific modulations of the TC PTP gene.

Characterization of CHO-K1 cells stably expressing PDE-IV enzymes. Whole-cell cAMP determinations vs broken-cell enzymatic assays.

A CHO-K1 cell line stably expressing a recombinant full-length human PDE-IVa (HSPDE4A4B) enzyme was established under hygromycin B selection. Full-length expression of the protein was determined by Western blot analysis, which revealed the presence of a 125-kDa immunoreactive band using rabbit anti-PDE-IVa antibodies. The potency of inhibitor compounds was examined by their ability to increase cAMP in the whole-cell, and by their ability to inhibit cAMP hydrolysis in a 100,000 g supernatant (soluble enzyme preparation) obtained from the same cell line. Inhibition of the expressed PDE-IVa activity by selective PDE-IV inhibitors--(R) and (S)-rolipram, RS 14203, and CDP 840--at 100 nM substrate demonstrated that RS 14203 and CDP 840 were the most potent with IC50 = 9 nM, followed by (R)-rolipram (IC50 = 110 nM) and (S)-rolipram (IC50 = 420 nM). The rank order of potencies of the inhibitors in elevating cAMP in the whole-cell assay was quite different from that on the soluble enzyme. RS 14203 was still the most potent compound in elevating cAMP. Moreover, the relative rank order of potencies between CDP 840 and (R)-rolipram changed dramatically, such that (R)-rolipram was more potent than CDP 840 = (S)-rolipram. An apparent 30-fold stereoselectivity between (R)- and (S)-rolipram was also noted. The whole-cell rank order of potencies was also maintained when PKA activity ratios were measured in place of cAMP levels. The ability of the compounds to elevate cAMP in the stable CHO-K1 cells appeared to track better with the potency of the compounds against the high-affinity (Sr) conformer of the enzyme rather than the low-affinity catalytic state.

Localization of phosphodiesterase-4 isoforms in the medulla and nodose ganglion of the squirrel monkey.

Pre-clinical and clinical studies are currently underway to evaluate the potential of phosphodiesterase-4 (PDE4) inhibitors for the treatment of chronic obstructive pulmonary disease and other inflammatory conditions of the airways. The most common side effect associated with this class of compounds is emesis. The squirrel monkey provides a model for evaluating the efficacy of PDE4 inhibitors and their emetic potential. The distribution of three PDE4 isoforms (A, C and D) has been investigated in the squirrel monkey medulla and nodose ganglion to determine which isoform(s) could be responsible for the emetic adverse effects. The distribution of PDE4 isoforms was delineated using immunohistochemistry with antibodies specific for PDE4A, PDE4C and PDE4D and by in situ hybridization with isoform-selective riboprobes. PDE4A was present in the medulla where expression was mostly restricted to glial cells and the vasculature. PDE4C was not detected in either the medulla or nodose ganglion. Finally, the PDE4D isoform was localized to neurons in the nodose ganglion and found through many structures of medulla including the area postrema, neurons of the nucleus tractus solitarius and locus coeruleus. These data are consistent with a role for PDE4D in the emetic response.

High-resolution linkage map in the proximity of the host resistance locus Cmv1.

The mouse chromosome 6 locus Cmv1 controls replication of mouse Cytomegalovirus (MCMV) in the spleen of the infected host. In our effort to clone Cmv1, we have constructed a high-resolution genetic linkage map in the proximity of the gene. For this, a total of 45 DNA markers corresponding to either cloned genes or microsatellites were mapped within a 7.9-cM interval overlapping the Cmv1 region. We have followed the cosegregation of these markers with respect to Cmv1 in a total of 2248 backcross mice from a preexisting interspecific backcross panel of 281 (Mus spretus x C57BL/6J)F1 x C57BL/6J and 2 novel panels of 989 (A/ J x C57BL6)F1 x A/J and 978 (BALB/c x C57BL/6J)F1 x BALB/c segregating Cmv1. Combined pedigree analysis allowed us to determine the following gene order and intergene distances (in cM) on the distal region of mouse chromosome 6: D6Mit216-(1.9)-D6Mit336-(2.2)- D6Mit218-(1.0)-D6Mit52-(0.5)-D6Mit194-(0.2)-Nkrp 1/ D6Mit61/135/257/289/338-(0.4)-Cmv1/Ly49A/D6Mit370++ +- (0.3)-Prp/Kap/D6Mit13/111/219-(0.3)-Tel/D6Mit374/290/ 220/196/195/110-(1.1)-D6Mit25. Therefore, the minimal genetic interval for Cmv1 of 0.7 cM is defined by 13 tightly linked markers including 2 markers, Ly49A and D6Mit370, that did not show recombination with Cmv1 in 1967 meioses analyzed; the proximal limit of the Cmv1 domain was defined by 8 crossovers between Nkrp1/ D6Mit61/135/257/289/338 and Cmv1/Ly49A/D6Mit370, and the distal limit was defined by 5 crossovers between Cmv1/Ly49A/D6Mit370 and Prp/Kap/D6Mit13/111/219. This work demonstrates tight linkage between Cmv1 and genes from the natural killer complex (NKC), such as Nkrp1 and Ly49A, suggesting that Cmv1 may represent an NK cell recognition structure encoded in the NKC region.

Structure of the murine MPTP-PEST gene: genomic organization and chromosomal mapping.

Protein tyrosine phosphatases comprise a large family of enzymes that are involved in the control of cellular tyrosine phosphorylation. We have used lambda phage analysis to elucidate the complete genomic structure of an intracellular member of this family, the murine MPTP-PEST gene. Eight overlapping lambda phage clones representing the MPTP-PEST locus were isolated from a 129/sv mouse genomic library. The gene spans over 90 kb of the mouse genome and is composed of 18 exons, 10 of which constitute the catalytic phosphatase domain. Detailed comparison of the position of intron/exon boundaries of the phosphatase domain of MPTP-PEST to those of several other protein tyrosine phosphatases indicates that the MPTP-PEST catalytic domain contains additional exons as a consequence of the insertion of novel introns. In addition, this analysis reveals a strong conservation of the genomic organization within the catalytic domain of the protein tyrosine phosphatase gene family. Finally, fluorescence in situ hybridization with MPTP-PEST genomic DNA refines the map position of MPTP-PEST to mouse chromosome 5A3 to B. This result is in agreement with the previous mapping of the human PEST gene to chromosome 7q11.23, a region of synteny with the centromeric portion of mouse chromosome 5.