Human SP-A 3′-UTR variants mediate differential gene expression in basal levels and in response to dexamethasone

Abstract

Human surfactant protein A (SP-A) is encoded by two genes ( SP-A1, SP-A2), and each is identified with several alleles. SP-A is involved in normal lung function, innate immunity, inflammatory processes, and is regulated by glucocorticoids. We investigated the role of 3′-untranslated region (UTR) of 10 SP-A variants on gene expression using transient transfection of 3′-UTR constructs in the human lung adenocarcinoma cell line NCI-H441. We found: 1) both basal mRNA and protein levels of the reporter gene of SP-A 3′-UTR constructs are significantly ( P < 0.01) reduced compared with controls (vector pGL3 and surfactant protein B pGL3) and that differences exist among alleles; and 2) after dexamethasone (Dex) treatment (100 nM for 16 h), mRNA was reduced (31–51%). Seven alleles showed a significant decrease ( P < 0.05) in mRNA, and three did not. Reporter activity was also decreased, from 17% (1A1) to 38% (1A), with six alleles showing a significant decrease. The data indicate that the 3′-UTR of SP-As play a differential role in SP-A basal expression and in response to Dex. Therefore, a careful consideration of individual use of steroid treatment may be considered.

SP-A1 and SP-A2 variants differentially enhance association ofPseudomonas aeruginosawith rat alveolar macrophages

“…Nucleotide or splice differences within regulatory [5Ј-untranslated region (UTR) and 3Ј-UTR] regions (13,15,32,40,54) have also been observed between the SP-A1 and SP-A2 genes and/or alleles. Quantitative differences include in vitro differences in basal mRNA levels and in response to dexamethasone (26,67) and differences in the SP-A mRNA (17,31) and protein (12,24,58) levels among individuals. The basis for the observed qualitative and quantitative differences may be genetic in nature (15,26,31,40,67).…”

Characterization of a human surfactant protein A1 (SP-A1) gene-specific antibody; SP-A1 content variation among individuals of varying age and pulmonary health

“…Moreover, qualitative and quantitative differences have been observed in vitro between the SP-A1 and SP-A2 genes (22,36,57,60,(77)(78)(79)(80)(81), pointing to the possibility that the overall functional activity of SP-A may depend on the relative SP-A1-to-SP-A2 levels rather than on the total SP-A content. To address this possibility, it .…”

“…Data from in vitro-expressed SP-A1 and SP-A2 variants showed that not only can homooligomers be formed, but these are also functional. In fact, functional (36,57,77) and regulatory (24,39,46,56) differences between SP-A1 and SP-A2 and/or among SP-A variants (78,79) have been observed. Therefore, we deemed it important to assess the SP-A gene-specific protein content in lung health and disease.…”

“…This may reflect the difference of regulatory mechanisms between human SP-A1 and SP-A2 during aging. Indeed, it has been observed that regulatory differences between human SP-A1 and SP-A2 exist in the transcriptional/pretranslational levels (38,39) as well as at the translational level (78,79). SP-A1 has been shown in vitro to be less active in host defense activities (36,57,80,81) compared with SP-A2.…”

“…More than 30 alleles have been characterized for these two genes, with four SP-A1 alleles (6A, 6A 2 , 6A 3 , and 6A 4 ) and six SP-A2 alleles (1A, 1A 0 , 1A 1 , 1A 2 , 1A 3 , and 1A 5 ) most frequently observed in the general population (10,14,16,40,67). Although a high level of sequence similarity is shared among the SP-A genes and their corresponding alleles, in vitro studies have identified both qualitative (22,36,57,60,77,80,81) and quantitative (24,35,38,46,56,69,70,78,79) differences between the two genes.…”