Martin Lipp

Roles of SLC/CCL21 and CCR7 in Human Kidney for Mesangial Proliferation, Migration, Apoptosis, and Tissue Homeostasis

The release of chemokines by intrinsic renal cells is an important mechanism for the regulation of leukocyte trafficking during renal inflammation. The expression of chemokine receptors by intrinsic renal cells such as mesangial cells (MC) suggests an expanded role for chemokine-chemokine receptor biology in local immunomodulation and potentially glomerular homeostasis. By immunohistochemistry we found the chemokine receptor CCR7 expressed in a mesangial pattern while the CCR7 ligand SLC/CCL21 showed a podocyte-specific expression. CCR7 expression was further characterized by RT-PCR, RNase protection assays, and FACS analysis of cultured human MC, and was found to be constitutively present. Real-time PCR of microdissected glomeruli confirmed the expression of SLC/CCL21. A functional role for CCR7 was demonstrated for human MC migration and proliferation. A protective effect of SLC/CCL21 was shown for MC survival in Fas Ab-induced apoptosis. Finally, “wound healing” was enhanced in the presence of SLC/CCL21 in an in vitro injury model. The constitutive glomerular expression of CCR7 and its ligand SLC/CCL21 in adjacent cell types of the human kidney suggests novel biological functions of this chemokine/chemokine receptor pair and a potential role in processes involved in glomerular homeostasis and regeneration.

Regulation of expression of chemokine receptor BLR1/CXCR5 during B cell maturation.

Functional interactions of chemokines and their receptors, which belong to the family of seven-transmembrane-domain proteins, signaling through heterotrimeric G proteins, have been shown to be primarily implicated in pathophysiological inflammatory processes [1]. Leukocytes are recruited from blood by locally produced chemokines towards sites of inflammation, arising from infections, injury, allergic reactions, arthritis and artherosclerosis. Several lines of evidence suggest that members of the chemokine receptor family may also be involved in lymphocyte migration to distinct lymphoid organs. Mature B and T lymphocytes continuously recirculate between blood and lymphatics to mediate immune surveillance. In this process they have to interact and to pass specialized endothelia: postcapillary venules in non-lymphoid organs and high endothelial venules in lymph nodes. Migration of B and T cells into secondary lymphatic organs is a prerequisite for the development of an antigen-specific immune response. The recent finding, that the chemokine receptor BLR1 is needed for B cell migration into lymphoid follicles [2], supports the view that chemokine receptors play an essential role as conductors of an orchestra of adhesion molecules, which allow lymphocyte subsets to navigate to different anatomical locations and are involved in the functional compartmentalization of lymphoid organs.

Cloning and chromosomal organization of a gene encoding a putative amino-acid permease from Saccharomyces cerevisiae.

A new member of the yeast amino acid (aa) permease gene family has been cloned, mapped and sequenced. The sequence of the PAP1 (putative aa permease 1) gene contains an open reading frame of 566 aa corresponding to a polypeptide with a calculated M(r) of 62,704. Its hydropathy profile suggests the presence of 13 membrane-spanning regions and a charged N-terminal domain. It does not resemble hydrophobic signal sequences found in secreted proteins. Hence, PAP1 encodes a protein with characteristics typical of integral membrane proteins translocating ligands across cellular membranes. Sequence comparisons indicate strong homology to the five known aa permeases of Saccharomyces cerevisiae and to an aa transporter in Trichoderma harzianum. Primer extension analysis revealed one major and one minor transcription start point located 121 and 125 nucleotides upstream from the ATG start codon, corresponding to a 2.1-kb transcript. PAP1 was mapped in a contig of three known (DBF4, TPI and HEM12), but so far unlinked, genes on chromosome IV.

Affinity Maturation in Ectopic Germinal Centers

It is becoming clear that a precisely structured lymphoid tissue is essential for the establishment of an antigen specific immune response. The differentiation of the antigen activated lymphocyte into effector cells requires a well organized microenvironment in which the antigen specific and the antigen presenting cells come into close physical contact. The central role of cytokines in lymphoid organogenesis and the important function of chemokines for guided cell movement into and within the secondary lymphoid organs are just emerging.

Akv murine leukemia virus enhances lymphomagenesis in myc-kappa transgenic and in wild-type mice

The contribution of endogenous retroviruses to the multistep process of lymphomagenesis was investigated in wild-type mice and in two different myc-kappa transgenic mouse lines by infection with Akv. This retrovirus is derived from the endogenous ecotropic provirus of the AKR mouse and was previously considered to be nonlymphomagenic. The mice of the two myc-k transgenic lines are predisposed to B-cell lymphomagenesis and were therefore considered to be more susceptible to Akv. For comparison, the same mouse strains were also infected with the exogenous Moloney murine leukemia virus (MoMuLV). Both MoMuLV and Akv increased the tumor incidence and shortened the tumor latency period in wild-type mice and in the transgenic mouse lines. The differences in pathogenicity, number of provirus integrations, and level of virus expression between MoMuLV and Akv indicate different mechanisms of lymphomagenesis: while MoMuLV induced tumors apparently by insertional mutagenesis involving common integration sites similar to previous reports, the enhancement of lymphomagenesis by Akv seems to be directed by other mechanisms.

Identification of a protein from Saccharomyces cerevisiae with E2F-like DNA-binding and transactivating properties

The promoter of the human proto‐oncogene MYC has been the first cellular target shown to be subject to regulation by the E2F transcription factor. E2F also has binding sites in other promoters regulated by cell proliferation and during the cell cycle. We have analyzed Saccharomyces cerevisiae for the presence of an E2F‐analogous protein. GAL1‐based promoter constructs carrying the E2F binding site of the MYC or the adenovirus E2 promoter showed transcriptional activity in yeast cells. A DNA‐binding factor, designated YE2F, binds specifically to the E2F consensus sequence and was partially purified from yeast extracts. YE2F showed identical contact points within the MYC binding site as authentic E2F protein from mammalian cells. The results suggest the existence of an E2F‐like protein in the yeast S. cerevisae.