A family of tissue-specific resistin-like molecules

Abstract

We have identified a family of resistin-like molecules (RELMs) in rodents and humans. Resistin is a hormone produced by fat cells. RELMalpha is a secreted protein that has a restricted tissue distribution with highest levels in adipose tissue. Another family member, RELMbeta, is a secreted protein expressed only in the gastrointestinal tract, particularly the colon, in both mouse and human. RELMbeta gene expression is highest in proliferative epithelial cells and is markedly increased in tumors, suggesting a role in intestinal proliferation. Resistin and the RELMs share a cysteine composition and other signature features. Thus, the RELMs together with resistin comprise a class of tissue-specific signaling molecules.

Figure 1

Identification and characterization of RELMα. (a) Predicted amino acid sequences of murine and rat RELMα. Identical amino acids are indicated, conservative substitutions are indicated by +, and conserved cysteine residues are shaded. (b) Schematic comparison of murine RELMα, rat RELMα, and murine resistin predicted amino acid sequences. Percent identity is indicated. (c and d) Northern blot analysis of RELMα gene expression in various mouse tissues (c) and a comparison of 3T3-L1 adipocytes and mouse white adipose tissue (WAT) (d). Ethidium bromide staining of 28S and 18S RNA is shown in each case.

Figure 2

RELMβ is an intestine-specific resistin-like molecule. (a) Murine RELMβ cDNA and protein sequences. In-frame upstream stop codon and putative polyadenylation sequence are underlined. Cysteine residues are indicated in bold, and the downstream stop codon is indicated by *. (b) Comparison of murine RELMβ and murine resistin predicted amino acid sequences. Percent identity is indicated. (c) Northern blot analysis of RELMβ gene expression in the mouse. 28S and 18S RNA is shown below to demonstrate loading of similar amounts of RNA (20 μg per lane). (d) Northern analysis of human RELMβ mRNA in multiple human tissues.

Figure 3

RELMβ is expressed in proliferative intestinal epithelia. (a) Northern analysis of RELMβ mRNA levels in mouse intestine. β-actin hybridization is shown as control for loading. (b) Northern analysis of RELMβ mRNA during mouse embryogenesis. (c and d) In situ hybridization of serial sections of mouse colon probed with RELMβ antisense (c) and sense (d) probes. Positive staining is dark blue. (e) Northern analysis of RELMβ in normal appearing small intestine (N) and adjacent tumors (T) in a min mouse. 28 and 18S RNA is shown as loading control. A representative of three independent experiments is shown.

Figure 4

The RELM family of secreted proteins. (a) RELMs are secreted proteins. RELMβ, RELMα, and resistin were fused to Flag epitope at C terminus and expressed in 293T cells. Media was sampled and analyzed by immunoblot using Flag antibody. − indicates control vector. (b) Consensus sequence of the RELM family. Blue shading indicates amino acid identity of two or more family members, aligned by dnastar megalign program using the Jotun Hein method. The signature sequence characteristic of the RELMs is indicated.