CP4: a pneumocyte-derived collagenous surfactant-associated protein. Evidence for heterogeneity of collagenous surfactant proteins

Abstract

Type II pneumocytes secrete pulmonary surfactant and are known to synthesize SP-35, a collagenous surfactant-associated protein. Freshly isolated type II cells also synthesize other bacterial collagenase-sensitive and hydroxyproline-containing proteins, including a glycoprotein designated CP4. CP4 was isolated from rat pneumocyte culture medium by immune precipitation with polyclonal antibodies to rat surfactant proteins or by DEAE chromatography and reverse-phase or gel permeation HPLC. CP4 did not cross-react with polyclonal antibodies to SP-35 and was completely resolved from SP-35 by SDS-PAGE (Mr 43K reduced) or isoelectric focusing. Unlike SP-35, which consists of acidic isoforms assembled as disulfide-bonded dimers and multimers, CP4 was secreted as basic isoforms assembled as disulfide-bonded trimers. Differences in primary structure were demonstrated by CNBr and V8 protease peptide mapping. The secretion of both proteins was inhibited by 2,2'-dipyridyl, an inhibitor of posttranslational prolyl and lysyl hydroxylation and collagen triple helix formation. CP4 was isolated from EDTA extracts of rat surfactant. These studies provide evidence for the heterogeneity of pneumocyte-derived collagenous surfactant-associated proteins.

Localization of Lung Surfactant Protein D on Mucosal Surfaces in Human Tissues

“…3 is one of the collectins, a family of oligomeric proteins whose individual chains consist of a collagen region linked to a C-type lectin domain via an ␣ helical neck region (1,2). The structural subunits of SP-D are homotrimers of these chains, and the subunits are themselves oligomerized into cross-like tetramers and higher oligomers (3)(4)(5)(6)(7)(8).…”

Investigations on Collectin Liver 1

“…C-type lectins bind, in a calcium-dependent manner, to targets presenting ligands with adequately spaced terminal carbohydrate groups (1). Although the first collectin identified, conglutinin, was reported 100 years ago (2), the study of collectins only took broader interest with the identification in 1978 of mannan-binding lectin (MBL) (3), followed by surfactant protein A (4) and surfactant protein D (5). Three further collectins were more recently discovered by Wakamiya and co-workers, i.e.…”

Serum levels of surfactant protein D predict the anti-tumor activity of gefitinib in patients with advanced non-small cell lung cancer

“…The serum SP-D level and mutation status were not related with overall survival in the extension study (data not shown). SP-D is the specific glycoprotein produced and secreted by normal alveolar type II cells and Clara cells, and it is responsible for the production of pulmonary surfactant protein [13,14]. Most SP-D can be both broken down by pulmonary macrophages and reabsorbed into the lamellar structures of type II cells as the pulmonary surfactant protein, while the remainder of it is transferred into the circulating blood; serum SP-D is well known as a marker of activity of interstitial lung diseases [18,19].…”