Isolation of a cDNA clone encoding a high molecular weight precursor to a 6-kDa pulmonary surfactant-associated protein

Differential Regulation of Human Surfactant Protein A Genes, SFTPA1 and SFTPA2, and Their Corresponding Variants

The human SFTPA1 and SFTPA2 genes encode the surfactant protein A1 (SP-A1) and SP-A2, respectively, and they have been identified with significant genetic and epigenetic variability including sequence, deletion/insertions, and splice variants. The surfactant proteins, SP-A1 and SP-A2, and their corresponding variants play important roles in several processes of innate immunity as well in surfactant-related functions as reviewed elsewhere [1]. The levels of SP-A have been shown to differ among individuals both under baseline conditions and in response to various agents or disease states. Moreover, a number of agents have been shown to differentially regulate SFTPA1 and SFTPA2 transcripts. The focus in this review is on the differential regulation of SFTPA1 and SFTPA2 with primary focus on the role of 5′ and 3′ untranslated regions (UTRs) and flanking sequences on this differential regulation as well molecules that may mediate the differential regulation.

Crystal-to-Crystal Synthesis of Triazole-Linked Pseudo-proteins via Topochemical Azide-Alkyne Cycloaddition Reaction

Isosteric replacement of amide bond(s) of peptides with surrogate groups is an important strategy for the synthesis of peptidomimetics (pseudo-peptides). Triazole is a well-recognized bio-isostere for peptide bonds, and peptides with one or more triazole units are of great interest for different applications. We have used a catalyst-free and solvent-free method, viz., topochemical azide-alkyne cycloaddition (TAAC) reaction, to synthesize pseudo-proteins with repeating sequences. A designed β-sheet-forming l-Ala-l-Val dipeptide containing azide and alkyne at its termini (N₃-Ala-Val-NHCH₂C≡CH, 1) was synthesized. Single-crystal XRD analysis of the dipeptide 1 showed parallel β-sheet arrangement along the b-direction and head-to-tail arrangement of such β-sheets along the c-direction. This head-to-tail arrangement along the c-direction places the complementary reacting motifs, viz., azide and alkyne, of adjacent molecules in proximity. The crystals of dipeptide 1, upon heating at 85 °C, underwent crystal-to-crystal polymerization, giving 1,4-triazole-linked pseudo-proteins. This TAAC polymerization was investigated by various time-dependent techniques, such as NMR, IR, DSC, and PXRD. The crystal-to-crystal nature of this transformation was revealed from polarizing microscopy and PXRD experiments, and the regiospecificity of triazole formation was evidenced from various NMR techniques. The MALDI-TOF spectrum showed the presence of pseudo-proteins >7 kDa.

Differential susceptibility of transgenic mice expressing human surfactant protein B genetic variants to Pseudomonas aeruginosa induced pneumonia

Surfactant protein B (SP-B) is essential for lung function. Previous studies have indicated that a SP-B 1580C/T polymorphism (SNP rs1130866) was associated with lung diseases including pneumonia. The SNP causes an altered N-linked glycosylation modification at Asn129 of proSP-B, e.g. the C allele with this glycosylation site but not in the T allele. This study aimed to generate humanized SP-B transgenic mice carrying either SP-B C or T allele without a mouse SP-B background and then examine functional susceptibility to bacterial pneumonia in vivo. A total of 18 transgenic mouse founders were generated by the DNA microinjection method. These founders were back-crossed with SP-B KO mice to eliminate mouse SP-B background. Four founder lines expressing similar SP-B levels to human lung were chosen for further investigation. After intratracheal infection with 50 μl of Pseudomonas aeruginosa solution (1 × 10(6) CFU/mouse) or saline in SP-B-C, SP-B-T mice the mice were sacrificed 24 h post-infection and tissues were harvested. Analysis of surfactant activity revealed differential susceptibility between SP-B-C and SP-B-T mice to bacterial infection, e.g. higher minimum surface tension in infected SP-B-C versus infected SP-B-T mice. These results demonstrate for the first time that human SP-B C allele is more susceptible to bacterial pneumonia than SP-B T allele in vivo.

Clinical, radiological and genetic analysis of a male infant with neonatal respiratory distress syndrome

Surfactant protein B (SP-B) deficiency has become increasingly recognized as a cause of severe prolonged respiratory distress. However, little has been reported with regard to the genetic variability of SP-B in Chinese infants with neonatal respiratory distress syndrome (RDS). One case of a Chinese male infant with neonatal RDS was analyzed for clinical manifestation and genetic variability of SP-B. The clinical manifestations, including grunting, intercostal retractions, nasal flaring, cyanosis and tachypnea were discovered in the physical examination. The initial chest X-ray indicated hyper-inflation, diffuse opacification and air bronchogram of the lungs. Pathological tests of lung tissue revealed RDS and SP-B deficiency. Atelectasis and pneumonedema were observed in the lobes of the lung. Molecular analysis of genomic DNA revealed a mutation of 121del2 in intron 4 of the SP-B gene. In conclusion, the variant in intron 4 of the SP-B gene was associated with neonatal RDS in a Chinese male infant.

Detection and localization of the hydrophobic surfactant proteins B and C in human tear fluid and the human lacrimal system

PURPOSE

To evaluate the expression and presence of the surfactant proteins (SP) B and C in the lacrimal apparatus at the ocular surface and in tear fluid.

METHODS

Expression of SP-B and SP-C was analyzed by RT-PCR in healthy lacrimal gland, conjunctiva, meibomian gland, accessory lacrimal glands, cornea, and nasolacrimal ducts. The deposition of the hydrophobic proteins SP-B and SP-C was determined by Western blot and immunohistochemistry in healthy tissues, tear fluid, and aqueous humor.

RESULTS

The presence of both SP-B and SP-C on mRNA and protein level was evidenced in healthy human lacrimal gland, conjunctiva, cornea, and nasolacrimal ducts. Moreover, both proteins were present in tear fluid but were absent in aqueous humor. Immunohistochemical investigations revealed production of both peptides by acinar epithelial cells of the lacrimal gland and additionally by accessory lacrimal glands of the eyelid as well as epithelial cells of the conjunctiva and nasolacrimal ducts. Immunohistochemically, healthy cornea and goblet cells revealed no reactivity.

CONCLUSIONS

Besides the recently detected surfactant-associated proteins SP-A and SP-D, our results show that SP-B and SP-C are also peptides of the tear film, the ocular surface, and the lacrimal apparatus. Based on the current knowledge of lowering surface tension in alveolar lung cells, a similar effect of SP-B and SP-C may be assumed concerning the tear film.

Surfactant protein B polymorphisms are associated with severe respiratory syncytial virus infection, but not with asthma

BACKGROUND

Surfactant proteins (SP) are important for the innate host defence and essential for a physiological lung function. Several linkage and association studies have investigated the genes coding for different surfactant proteins in the context of pulmonary diseases such as chronic obstructive pulmonary disease or respiratory distress syndrome of preterm infants. In this study we tested whether SP-B was in association with two further pulmonary diseases in children, i. e. severe infections caused by respiratory syncytial virus and bronchial asthma.

METHODS

We chose to study five polymorphisms in SP-B: rs2077079 in the promoter region; rs1130866 leading to the amino acid exchange T131I; rs2040349 in intron 8; rs3024801 leading to L176F and rs3024809 resulting in R272H. Statistical analyses made use of the Armitage's trend test for single polymorphisms and FAMHAP and FASTEHPLUS for haplotype analyses.

RESULTS

The polymorphisms rs3024801 and rs3024809 were not present in our study populations. The three other polymorphisms were common and in tight linkage disequilibrium with each other. They did not show association with bronchial asthma or severe RSV infection in the analyses of single polymorphisms. However, haplotypes analyses revealed association of SP-B with severe RSV infection (p = 0.034).

CONCLUSION

Thus our results indicate a possible involvement of SP-B in the genetic predisposition to severe RSV infections in the German population. In order to determine which of the three polymorphisms constituting the haplotypes is responsible for the association, further case control studies on large populations are necessary. Furthermore, functional analysis need to be conducted.

Family-based association tests suggest linkage between surfactant protein B (SP-B) (and flanking region) and respiratory distress syndrome (RDS): SP-B haplotypes and alleles from SP-B-linked loci are risk factors for RDS

Genetic variants of surfactant protein B (SP-B) have been associated with respiratory distress syndrome (RDS) in the prematurely born infant. We wished to determine linkage between RDS and SP-B single nucleotide polymorphisms (SNPs) [-18 (A/C), 1013 (A/C), 1580 (C/T), and 9306 (A/G)] or SP-B-linked microsatellite [(D2S388, D2S2232, (AAGG)n, and GATA41E01 (or D2S1331)] loci and identify susceptibility or protective alleles and haplotypes. We genotyped 132 families consisting of one or two parents and at least one child affected with RDS and performed biallelic and multiallelic family-based association test (FBAT) analysis, and extended transmission disequilibrium test (ETDT). ETDT analysis identified the microsatellite SP-B-linked loci (except D2S2232) to be linked to RDS. One allele from each of these three marker loci contributes to the risk of RDS. Multiallelic FBAT analysis detected a signal of linkage for the region of the four SNP loci. Three haplotypes within this region contribute to RDS risk. Although no other region showed significant linkage as judged by multiallelic FBAT, biallelic FBAT analysis revealed three potential susceptibility haplotypes formed by two to four loci within the SP-B and SP-B-linked microsatellite region. Each haplotype included GATA41E01, which was identified by ETDT analysis to be linked to RDS. We conclude that SP-B or SP-B-linked loci are linked to RDS and certain alleles or haplotypes are susceptibility or protective factors for the development of RDS in infants born prematurely.

Deletions within a CA-repeat-rich region of intron 4 of the human SP-B gene affect mRNA splicing

Length variants within a CA-repeat-rich region of intron 4 of the human SP-B (pulmonary surfactant protein-B) gene are associated with several lung diseases. The hypothesis that SP-B intron 4 affects mRNA splicing was studied. SP-B minigenes containing exons 1-6 with a normal-sized intron 4 (pBi4normal) or intron 4 containing deletions (pBi4del) of 193, 211, 264 or 340 bp were expressed in CHO (Chinese hamster ovary) cells by transient transfection. Two forms of SP-B transcripts, normal and incompletely spliced, were detected. With pBi4normal, normal-sized SP-B mRNA was the predominant form and a very low amount of incompletely spliced mRNA was present, whereas with the pBi4del variants the amount of normal SP-B mRNAs was lower and the amount of incompletely spliced mRNA was relatively high. Reverse transcription-PCR results and sequencing data indicated that the incompletely spliced SP-B RNA contained intron 4 sequence, and this incompletely spliced RNA was also observed in normal lung. Lung cancer tissues with intron 4 deletions exhibited a larger amount of abnormally spliced RNAs compared with normal lung tissue or cancerous tissue with normal-sized intron 4. The results indicate that intron 4 length variants affect SP-B mRNA splicing, and that this may contribute to lung disease.

Genetic polymorphisms in sepsis

CONTEXT

Wide variability exists in the susceptibility to and outcome from sepsis even within similar intensive care unit populations. Some of this variability in the host may be due to genetic variation in genes coding for components of the innate immune response.

OBJECTIVE

To review the evidence for a genetic influence on the susceptibility to and outcome from sepsis.

DESIGN

Literature review.

PATIENTS

Variety of adult and pediatric patients with various critical illnesses and infections.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Susceptibility to clinical symptoms of sepsis and outcome as measured by severity of disease and mortality.

RESULTS

Polymorphisms in genes coding for proteins involved in the recognition of bacterial pathogens (Toll-like receptor 4, CD14, Fc(gamma)RIIa, and mannose-binding lectin) and the response to bacterial pathogens (tumor necrosis factor-alpha, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor agonist, IL-6, IL-10, heat shock proteins, angiotensin I converting enzyme, plasminogen activator inhibitor-1) can influence the amount or function of the protein produced in response to bacterial stimuli. Evidence is discussed suggesting that some of these genetic polymorphisms influence the susceptibility to and outcome from sepsis.

CONCLUSION

Host genetic variability in the regulatory and coding regions of genes for components of the innate immune system may influence the susceptibility to and/or outcome from sepsis. The disparate results observed in many studies of polymorphisms in sepsis emphasize the need for future studies to be larger, to include the analysis of multiple polymorphisms, and to be better designed with respect to control populations to identify the degree of influence that genetic variability has on sepsis.

Association between surfactant protein B + 1580 polymorphism and the risk of respiratory failure in adults with community-acquired pneumonia

OBJECTIVE

Pulmonary surfactant protein (SP)-B plays a vital role in the formation and function of surfactant in the lung. A genetic polymorphism (SP-B + 1580) is postulated to result in diminished activity of SP-B. The objective was to determine whether the SP-B + 1580 CC genotype is associated with an increased risk of respiratory failure and ARDS in adults with community-acquired pneumonia.

DESIGN

Prospective cohort of adults diagnosed with community-acquired pneumonia.

SETTING

Hospital system.

PATIENTS

We enrolled 402 adults > or = 18 yrs of age with community-acquired pneumonia; 158 were white, 243 were African American, and one was Asian.

INTERVENTIONS

Genotypic analysis was performed on DNA isolated from whole blood using polymerase chain reaction amplification and DdeI restriction enzyme digestion.

MEASUREMENTS AND MAIN RESULTS

We recorded the requirement for mechanical ventilation, the presence of acute respiratory distress syndrome (ARDS) or septic shock, and mortality. Sixty-three patients required mechanical ventilation, 12 patients developed ARDS, and 35 patients developed septic shock. Genotypic frequencies at the SP-B + 1580 site were T/T 183 of 402 (0.45), T/C 160 of 402 (0.40), and C/C 59 of 402 (0.15). Of the 59 patients who were C/C at the SP-B + 1580 site, 21 (0.356) required mechanical ventilation, compared with 26 of 160 patients (0.163) who were T/C and 16 of 183 (0.087) patients who were T/T (p < .001). ARDS developed in five of 59 (0.085) patients with the C/C genotype, compared with six of 160 (.038) patients with T/C and one of 183 patients with T/T (0.005, p < .009). Septic shock occurred in 12 of 59 (0.203) patients with the C/C genotype, compared with 13 of 160 (0.081) patients with T/C and ten of 183 (0.055) patients with T/T (p < .001). Mortality rate was not different between the three genotypes.

CONCLUSION

Carriage of the C allele at the SP-B + 1580 site is associated with ARDS, septic shock, and the need for mechanical ventilation in adults with community-acquired pneumonia.

Alterations in SP-B and SP-C expression in neonatal lung disease

The hydrophobic surfactant proteins, SP-B and SP-C, have important roles in surfactant function. The importance of these proteins in normal lung function is highlighted by the lung diseases associated with abnormalities in their expression. Mutations in the gene encoding SP-B result in severe, fatal neonatal lung disease, and mutations in the gene encoding SP-C are associated with chronic interstitial lung diseases in newborns, older children, and adults. This work reviews the current state of knowledge concerning the lung diseases associated with mutations in the SP-B and SP-C genes, and the potential roles of abnormal SP-B and SP-C expression and genetic variation in these genes in other lung diseases.

Involvement of napsin A in the C- and N-terminal processing of surfactant protein B in type-II pneumocytes of the human lung

Surfactant protein B (SP-B) is a critical component of pulmonary surfactant, and a deficiency of active SP-B results in fatal respiratory failure. SP-B is synthesized by type-II pneumocytes as a 42-kDa propeptide (proSP-B), which is posttranslationally processed to an 8-kDa surface-active protein. Napsin A is an aspartic protease expressed in type-II pneumocytes. To characterize the role of napsin A in the processing of proSP-B, we colocalized napsin A and precursors of SP-B as well as SP-B in the Golgi complex, multivesicular, composite, and lamellar bodies of type-II pneumocytes in human lungs using immunogold labeling. Furthermore, we measured aspartic protease activity in isolated lamellar bodies as well as isolated human type-II pneumocytes and studied the cleavage of proSP-B by napsin A and isolated lamellar bodies in vitro. Both, napsin A and isolated lamellar bodies cleaved proSP-B and generated three identical processing products. Processing of proSP-B by isolated lamellar bodies was completely inhibited by an aspartic protease inhibitor. Sequence analysis of proSP-B processing products revealed several cleavage sites in the N- and C-terminal propeptides as well as one in the mature peptide. Two of the four processing products generated in vitro were also detected in type-II pneumocytes. In conclusion, our results show that napsin A is involved in the N- and C-terminal processing of proSP-B in type-II pneumocytes.

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

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% (1A(1)) 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.

Surfactant-associated proteins: functions and structural variation

Pulmonary surfactant is a barrier material of the lungs and has a dual role: firstly, as a true surfactant, lowering the surface tension; and secondly, participating in innate immune defence of the lung and possibly other mucosal surfaces. Surfactant is composed of approximately 90% lipids and 10% proteins. There are four surfactant-specific proteins, designated surfactant protein A (SP-A), SP-B, SP-C and SP-D. Although the sequences and post-translational modifications of SP-B and SP-C are quite conserved between mammalian species, variations exist. The hydrophilic surfactant proteins SP-A and SP-D are members of a family of collagenous carbohydrate binding proteins, known as collectins, consisting of oligomers of trimeric subunits. In view of the different roles of surfactant proteins, studies determining the structure-function relationships of surfactant proteins across the animal kingdom will be very interesting. Such studies may reveal structural elements of the proteins required for surface film dynamics as well as those required for innate immune defence. Since SP-A and SP-D are also present in extrapulmonary tissues, the hydrophobic surfactant proteins SP-B and SP-C may be the most appropriate indicators for the evolutionary origin of surfactant. SP-B is essential for air-breathing in mammals and is therefore largely conserved. Yet, because of its unique structure and its localization in the lung but not in extrapulmonary tissues, SP-C may be the most important indicator for the evolutionary origin of surfactant.

Granulysin: a novel antimicrobial

Granulysin is a novel lytic molecule produced by human cytolytic T-lymphocytes (CTLs) and natural killer (NK) cells. It is active against a broad range of microbes, including Gram-positive and -negative bacteria, parasites and Mycobacterium tuberculosis. It is functionally related to other antibacterial peptides, like defensins and magainins, but is structurally distinct. It has structural similarity to porcine NK-lysin and to amoebapores made by Entamoeba histolytica. Synthetic peptides derived from granulysin have differential activity against eukaryotic cells and bacteria. Selective bactericidal peptides may have therapeutic roles as novel antibiotics.

Polymorphisms of human SP-A, SP-B, and SP-D genes: association of SP-B Thr131Ile with ARDS

An allele association study of 19 polymorphisms in surfactant proteins SP-A1, SP-A2, SP-B, and SP-D genes in acute respiratory distress syndrome (ARDS) was carried out. Trend-test analysis revealed differences (p < 0.05) in the frequency of alleles for some of the microsatellite markers flanking SP-B, and for one polymorphism (C/T) at nucleotide 1580 [C/T (1580)], within codon 131 (Thr131Ile) of the SP-B gene. The latter determines the presence or absence of a potential N-linked glycosylation site. Multivariate analysis revealed significant differences only for the C/T (1580) polymorphism. When the ARDS population was divided into subgroups, idiopathic (i.e., pneumonia, etc.) or exogenic (i.e., trauma, etc.), significant differences were observed for the C/T (1580), for the idiopathic ARDS group, and the frequency of the C/C genotype was increased in this group. Based on the odds ratio, the C allele may be viewed as a susceptibility factor for ARDS. Although the expression of both C and T alleles occurs in heterozygous individuals, it is currently not known whether these alleles correspond to similar levels of SP-B protein. These data suggest that SP-B or a linked gene contributes to susceptibility to ARDS.

Prolonged survival in hereditary surfactant protein B (SP-B) deficiency associated with a novel splicing mutation

Hereditary surfactant protein B (SP-B) deficiency has been lethal in the first year of life without lung transplantation. We tested the hypothesis that SP-B gene mutations may result in milder phenotypes by investigating the mechanisms for lung disease in two children with less severe symptoms than have been previously observed in SP-B deficiency. Immunostaining patterns for pulmonary surfactant proteins were consistent with SP-B deficiency in both children. DNA sequence analysis indicated that both children were homozygous for a mutation in exon 5 that created an alternative splice site. Reverse transcriptase PCR and sequence analysis confirmed use of this splice site, which resulted in a frameshift and a premature termination codon in exon 7. The predominant reverse transcriptase PCR product, however, lacked exon 7, which restored the reading frame but would not allow translation of the exons that encode mature SP-B. Western blot analysis detected reduced amounts of mature SP-B as well as an aberrant SP-B proprotein that corresponded to the size expected from translation of the abnormal transcript. We conclude that a novel splicing mutation was the cause of lung disease in these children and that hereditary SP-B deficiency can be the cause of lung disease in older children.

Aberrant SP-B mRNA in lung tissue of patients with congenital alveolar proteinosis (CAP)

Mutations in the surfactant protein (SP)-B gene are responsible for SP-B deficiency in congenital alveolar proteinosis (CAP) (Nogee et al. J Clin Invest 1994: 93: 1860-1883; Lin et al. Mol Genet Metab 1998: 64: 25-35; Klein et al. Pediatrics 1998: 132: 244-248; Ballard et al. Pediatrics 1995: 96: 1046-1052). The multigenerational consanguineous pedigree under study does not carry any of the known mutations, although this pedigree had 14 infant deaths following respiratory distress at birth. Immunostaining of the lungs from three such infants revealed decreased or absent SP-B. By sequencing of SP-B exons, exon-intron junctions, and the 5' and 3' flanking regions, nine polymorphisms were found in this pedigree, but none of them could explain the observed SP-B deficiency. Further analysis of SP-B mRNA by reverse transcription-polymerase chain reaction from paraffin-embedded lung tissue of CAP patients showed that SP-B mRNA is not intact. Although the sequence of mRNA from exon 1-exon 7 and from exon 8-exon 10 could be amplified, the region between exons 7 and 8 could not. From fluorescence in situ hybridization of the short arm of chromosome 2p, only 2 signals were identified, eliminating the possibility of translocation as the cause of the SP-B mRNA aberrance. Although the nature of the genetic basis of SP-B deficiency in this family is currently unknown, the existence of aberrant SP-B mRNA may, at least in part, be responsible for the SP-B deficiency in this pedigree.

cDNA cloning of ovine pulmonary SP-A, SP-B, and SP-C: isolation of two different sequences for SP-B

Pulmonary surfactant promotes alveolar stability by lowering the surface tension at the air-liquid interface in the peripheral air spaces. The three surfactant proteins SP-A, SP-B, and SP-C contribute to dynamic surface properties involved during respiration. We have cloned and sequenced the complete cDNAs for ovine SP-A and SP-C and two distinct forms of ovine SP-B cDNAs. The nucleotide sequence of ovine SP-A cDNA consists of 1,901 bp and encodes a protein of 248 amino acids. Ovine SP-C cDNA contains 809 bp, predicting a protein of 190 amino acids. Ovine SP-B is encoded by two mRNA species, which differ by a 69-bp in-frame deletion in the region coding for the active airway protein. The larger SP-B cDNA comprises 1,660 bp, encoding a putative protein of 374 amino acids. With the sequences reported, a more complete analysis of surfactant regulation and the determination of their physiological function in vivo will be enabled.

Allelic heterogeneity in hereditary surfactant protein B (SP-B) deficiency

Inability to produce surfactant protein B (SP-B) causes fatal neonatal respiratory disease. A frame-shift mutation (121ins2) is the predominant but not exclusive cause of disease. To determine the range of mechanisms responsible for SP-B deficiency, both alleles from 32 affected infants were characterized. Sixteen infants were homozygous for the 121ins2 mutation, 10 infants were heterozygous for the 121ins2 and another mutation, and six infants were homozygous for other mutations. Thirteen novel SP-B gene mutations were identified, which were not found in a control population. One novel mutation was found in two unrelated families. Surfactant protein expression was evaluated by immunohistochemistry and/or protein blotting. Absence of proSP-B and mature SP-B was associated with nonsense and frame-shift mutations. In contrast, proSP-B expression was associated with missense mutations, or mutations causing in-frame deletions or insertions, and low levels of mature SP-B expression were associated with four mutations. Extracellular staining for proSP-C and/or aberrantly processed SP-C was observed in lungs of all infants with SP-B gene mutations. Hereditary SP-B deficiency is caused by a variety of distinct mutations in the SP-B gene and may be associated with reduced, as well as absent, levels of mature SP-B, likely caused by impaired processing of proSP-B.

Granulysin: a novel antimicrobial peptide of cytolytic T lymphocytes and natural killer cells

Granulysin is a novel antimicrobial protein produced by human cytolytic T lymphocytes and natural killer cells. It is active against a broad range of microbes, including Gram-positive and Gram-negative bacteria, fungi, and parasites. The fact that it kills Mycobacterium tuberculosis is particularly important, since the current vaccine (Bacille Calmette-Guerin, BCG) is of limited efficacy and antibiotic resistance is increasing. Although functionally related to other antibacterial peptides, defensins and magainins, granulysin is structurally distinct. Like porcine NK lysin and amoebapores made by Entamoeba histolytica, granulysin is related to saposins, small lipid-associated proteins present in the central nervous system. The identification of this novel molecule indicates a broader and perhaps more significant role for T lymphocytes in both innate and acquired antimicrobial defenses.

Retinoic acid stimulation of the human surfactant protein B promoter is thyroid transcription factor 1 site-dependent

Surfactant B (SP-B) is a 79-amino acid peptide critical to postnatal respiratory adaptation. Expression of SP-B by respiratory epithelial cells is regulated by developmental and hormonal influences at the level of gene transcription. Previous studies supported the role of retinoic acids (RA) and their receptors (RARs) in SP-B gene transcription. In the present study, RARalpha was detected in mouse alveolar type II epithelial cells where SP-B is synthesized and processed. Deletion and site-specific mutagenesis analysis identified clustered retinoic acid-responsive element sites in the 5'-flanking enhancer region of the hSP-B gene that bound RARalpha proteins. RAR coactivators ACTR, SRC-1, and transcriptional intermediary factor 2 (TIF2) stimulated human (h) SP-B promoter activity in a dose-dependent fashion in pulmonary adenocarcinoma H441 cells. In addition, an RAR-associated protein, CREB-binding protein (CBP), potentiated the effects of RAR on hSP-B promoter activity in H441 cells. Importantly, RA stimulation of the hSP-B promoter depends on tissue-specific thyroid transcription factor (TTF-1) DNA-binding sites. TTF-1 protein synergistically stimulated the hSP-B promoter with RARalpha, CBP, and nuclear receptor coactivators in H441 cells. In addition, TTF-1 interacted directly with RARalpha and TIF2 in the mammalian two-hybrid system. These findings support a model in which RAR/retinoid X receptor, TTF-1, coactivators, and CBP form a transcription activation complex in the upstream enhancer region of the hSP-B gene.

Structure and properties of surfactant protein B

Surfactant protein B is a small homodimeric protein that is found tightly associated with surfactant lipids in the alveolar space. In this review, we discuss the actions of SP-B on phospholipid membranes using information predominantly obtained from model membrane systems. We try to correlate these model actions with current concepts of SP-B structure and proposed biological functions. These functions may include critical roles in the intracellular assembly of surfactant through a role in lamellar body organogenesis, the structural rearrangement of secreted surfactant lipids into tubular myelin, and the subsequent rapid insertion of secreted surfactant phospholipids into the surface film itself. The relevance of SP-B to human biology is emphasized by the fatal respiratory distress that is associated with a genetic deficiency of SP-B and the important role of SP-B in certain exogenous surfactant formulations in wide clinical use.

Synthesis, processing and secretion of surfactant proteins B and C

Two small, hydrophobic peptides, surfactant protein (SP)-B and SP-C, play important roles in the generation and maintenance of a surface active film in the alveolus. Isolation and characterization of the cDNAs encoding SP-B and SP-C indicate that both peptides are synthesized as larger proproteins which are proteolytically processed to peptides with Mr approx. 8000 and 4000, respectively. The biosynthetic pathway leading to generation and secretion of the biophysically active mature SP-B and SP-C peptides is reviewed.

Surfactant proteins: molecular genetics of neonatal pulmonary diseases

Genetic and phenotypic complexity has been described for diseases of varied etiology. Groups of patients with varied phenotype can be used in association studies as an initial approach to identify contributing loci. Although association studies have limitations, their value is enhanced by using candidate genes with functions related to disease. Surfactant proteins have been studied in the etiopathogenesis of neonatal pulmonary diseases. SP-A and SP-B polymorphisms are found at a higher frequency in certain groups of patients with respiratory distress syndrome (RDS), and SP-B mutations are linked to the pathogenesis of congenital alveolar proteinosis (CAP). Phenotypic heterogeneity is observed for both CAP and RDS. The available data suggest that a number of factors contribute to the etiology of CAP and RDS and, therefore, a multidisciplinary approach of clinical, genetic, epidemiologic, and statistical considerations is necessary for an in-depth understanding of the pathophysiology of these and other pulmonary diseases.

Secondary structure and limited proteolysis give experimental evidence that the precursor of pulmonary surfactant protein B contains three saposin-like domains

The 42 kDa precursor of surfactant protein B generates the 79 residue mature SP-B polypeptide, which belongs to the family of saposin-like proteins and has unique functional roles in pulmonary surfactant. From sequence comparisons it has been suggested that proSP-B, in addition to SP-B, contains two saposin-like domains, but their existence has until now not been experimentally verified. The 381 residue human proSP-B was now fused to an N-terminal poly-His tag, expressed in Escherichia coli, and purified from inclusion bodies by resolubilisation with 2.5% (w/v) SDS and, after removal of SDS, subsequent metal affinity chromatography. Recombinant proSP-B thus obtained exhibits about 35% alpha-helical structure in sodium phosphate buffer and is proteolytically cleaved preferentially between the three saposin-like domains. These results experimentally support that proSP contains, in addition to SP-B, two further saposin-like domains.

Synthetic mimics of surfactant proteins B and C: in vitro surface activity and effects on lung compliance in two animal models of surfactant deficiency

Synthetic surfactant peptides SP-B1-78 and SP-C1-31 in a standard phospholipid mixture have been employed to examine the correlation between in vitro surface activity and in vivo function of synthetic surfactant preparations in the isolated rat lung and premature rabbit models of respiratory distress syndrome. Monolayer techniques showed that SP-B peptides have a high propensity for association with a phospholipid structure. By dynamic respreading, synthetic SP-B and SP-C showed rapid spreading and attained low surface tensions. Used as replacement surfactants in two animal models, these synthetic surfactant preparations partially restored lung compliance in lavaged rats and premature rabbits better than a pure phospholipid preparation and to a degree comparable to clinical surfactant, measured by pressure/volume curves. Our data confirm that in vitro functional determinations of synthetic surfactant peptides are instrumental in the preparation of replacement surfactants, and that dispersions thus selected represent viable therapeutic alternatives to current treatments for respiratory distress syndrome.

Molecular structures and interactions of pulmonary surfactant components

The dominating functional property of pulmonary surfactant is to reduce the surface tension at the alveolar air/liquid interface, and thereby prevent the lungs from collapsing at the end of expiration. In addition, the system exhibits host-defense properties. Insufficient amounts of pulmonary surfactant in premature infants causes respiratory distress syndrome, a serious threat which nowadays can be effectively treated by airway instillation of surfactant preparations. Surfactant is a mixture of many molecular species, mainly phospholipids and specific proteins, surfactant protein A (SP-A), SP-B, SP-C and SP-D. SP-A and SP-D are water-soluble and belong to the collectins, a family of large multimeric proteins which structurally exhibit collagenous/lectin hybrid properties and functionally are Ca2+-dependent carbohydrate binding proteins involved in innate host-defence functions. SP-A and SP-D also bind lipids and SP-A is involved in organization of alveolar surfactant phospholipids. SP-B belongs to another family of proteins, which includes also lipid-interacting polypeptides with antibacterial and lytic properties. SP-B is a 17.4-kDa homodimer and each subunit contains three intrachain disulphides and has been proposed to contain four amphipathic helices oriented pairwise in an antiparallel fashion. SP-A, SP-B and SP-D all have been detected also in the gastrointestinal tract. SP-C, in contrast, appears to be a unique protein with extreme structural and stability properties and to exist exclusively in the lungs. SP-C is a lipopeptide containing covalently linked palmitoyl chains and is folded into a 3.7-nm alpha-helix with a central 2.3-nm all-aliphatic part, making it perfectly suited to interact in a transmembranous way with a fluid bilayer composed of dipalmitoylglycerophosphocholine, the main component of surfactant. Homozygous genetic deficiency of proSP-B causes lethal respiratory distress soon after birth and is associated with aberrant processing of the precursor of SP-C. This review focuses on the chemical composition, structures and interactions of the pulmonary surfactant, in particular the associated proteins.

Efficacy of synthetic peptide-containing surfactant in the treatment of respiratory distress syndrome in preterm infant rhesus monkeys

Studies were conducted to assess the efficacy and safety of a synthetic peptide-containing surfactant in the treatment of respiratory distress syndrome (RDS) in preterm (approximately 80% of normal gestation) infant rhesus monkeys. Surfactant was prepared consisting of the phospholipids dipalmitoylphosphatidyl choline and palmitoyl-oleoyl phosphatidyl glycerol and a synthetic peptide modeled after surfactant protein B (SP-B), "KL4-Surfactant" contained a peptide having the sequence KLLLLKLLLLKLLLLKLLLLK, where "K" is lysine and "L" is leucine. The peptide was selected because it mimics the repeating stretches of hydrophobic residues with intermittent basic hydrophilic residues seen in SP-B. KL4-Surfactant was shown to have biophysical activity assessed as the ability to lower surface tension at an air-liquid interface in a pulsating bubble surfactometer. Thirty premature rhesus monkeys were treated shortly after birth with one dose of KL4-Surfactant. The arterial to alveolar oxygen partial pressure ratio (a/A) was found to rise from a pretreatment level of 0.11 +/- 0.01 (mean +/- SEM), indicative of severe RDS, to 0.40 +/- 0.02 at 12-13 h post-treatment. The improvement in oxygenation persisted throughout the study period, with a mean a/A at 22-23 h of 0.45 +/- 0.07. Chest radiographs and gross and microscopic examination of the lungs all confirmed the reversal of the atelectasis seen before treatment. Animals treated with a dose of 200 mg/kg showed a faster, more consistent, and greater response than did a group treated with an average dose of 127 mg/kg. There was no evidence of toxicity after treatment with the higher dose as demonstrated by physiologic, hematologic, biochemical, and pathologic data. The importance of the peptide in the synthetic surfactant was apparent from the results obtained with a control group of nine premature monkeys treated with a non-peptide-containing surfactant; the a/A of this group was 0.15 +/- 0.03 at nine hours of age as compared with a value of 0.38 +/- 0.02 for 30 comparable animals receiving KL4-Surfactant.

Protein-phospholipid interactions in pulmonary surfactant. The Parker B. Francis Lectureship

SP-B is the protein in pulmonary surfactant with the greatest capacity to augment the phospholipids, ability to resist surface tension, and capability to prevent collapse of pulmonary alveoli. Synthetic peptides derived from the structure of SP-B and simplified analogues of these SP-B-derived peptides were found by tryptophan fluorescence to partition within the phospholipid layer in contact with both polar head groups and acyl side chains of the phospholipids. The intermittent hydrophilic basic residues were found to be essential for full activity, probably because of electrostatic interactions formed with phosphates of the polar head groups. The hydrophobic stretches of residues in SP-B and the related peptides supplement the activity through interaction with the phospholipid acyl side chains. By increasing intermolecular and intramolecular order of the phospholipid layer and thereby stability of the layer, the SP-B analogues provide strong surfactant activity. Simplified peptide analogues of SP-B, dispersed in DPPC and POPG, provide strong surfactant activity in vitro and in the lungs of premature infant rabbits, rhesus monkeys, and humans.

Amphipathic alpha-helical peptides based on surfactant apoprotein SP-A

Three peptides based on the putative amphipathic helical region of the major pulmonary surfactant apoprotein (SP-A) were synthesized by solid-phase techniques, mixed with DPPC and tested for efficacy as lung surfactants in an in vitro adult rat lavaged lung model. The peptides correspond to residues 81-102 (SP-A81-102) and 78-101 (SP-A78-101) of the native human sequence and an analog with increased hydrophobicity, Leu84,90SP-A78-101. Neither native sequence was effective in simple mixtures with DPPC. However, substitution of leucine residues for Asp84 and Thr90 of SP-A81-102 yielded a peptide which was active in mixtures with DPPC, restoring quasi-static lung compliance to 90% of the unlavaged value. In the absence of peptide, DPPC had no effect on the P-V curve of the lavaged lung. The activity of the Leu84,90 analog correlated with an increased amphipathic alpha-helical potential and an improvement in several predictive parameters for lipid-binding. The similarities between this active peptide and other active amphipathic alpha-helical peptides lend support to the hypothesis that amphipathic alpha-helical potential and the size of the hydrophobic face are critical for functional synthetic surfactant peptides in simple mixtures with dipalmitoylphosphatidylcholine.

Human surfactant polypeptide SP-B. Disulfide bridges, C-terminal end, and peptide analysis of the airway form

Human hydrophobic surfactant polypeptide, SP-B, purified from lung tissue by exclusion chromatography in organic solvents, has been characterized. The polypeptide is 79 residues long, has a C-terminal methionine, and contains seven Cys residues. Native human SP-B lacks free thiol groups. Three intrachain disulfide bridges were defined, linking Cys8 to Cys77, Cys11 to Cys71 and Cys35 to Cys46. The remaining Cys48 is concluded to link the protein chains into homodimers via an interchain disulfide to its counterpart in a second SP-B polypeptide. These SS bridges are identical to those in the porcine form and confirm a consestant and unique disulfide pattern for SP-B polypeptides in general.

Localization of pulmonary surfactant proteins using immunohistochemistry and tissue in situ hybridization

Surfactant, a complex mixture of lipids and proteins, is produced by the type II alveolar epithelial cells. Numerous studies have localized surfactant protein A (SP-A) to type II cells of the lung, and recent studies have shown that the type II cells in the human lung are also the site of synthesis of SP-B, one of the hydrophobic surfactant proteins. There have been conflicting reports about additional sites of SP-A production. We have studied the localization of the mRNAs for SP-A, SP-B, and SP-C in the rat and for SP-C in the human lung by tissue in situ hybridization using cRNA probes. The mRNAs for all three rat surfactant proteins and for human SP-C were found in type II alveolar epithelial cells. In addition, the mRNAs for rat SP-A and SP-B were found in nonciliated bronchiolar cells. SP-C mRNA was not detectable in the bronchiolar cells of both rat and human lung tissue. Immunohistochemical studies in the rat lung with antisera to SP-A and SP-B confirmed the presence of the protein in cell types where the mRNA was found, as well as in some alveolar macrophages. Alveolar macrophages in both rat and human lung tissue were negative for all mRNAs. Further studies are required to ascertain whether there are differences in the processing, function, and regulation of these proteins in the different cell types that produce them.

Surfactant protein B: disulfide bridges, structural properties, and kringle similarities

The disulfide bridges in porcine hydrophobic surfactant protein B (SP-B) were determined. Results show that three intrachain bridges link half-cystine residues 8 and 77, 11 and 71, and 35 and 46, respectively. This gives SP-B an appearance of three loops, a central big loop surrounded by two smaller ones. In the major form of SP-B, the remaining half-cystine, Cys-48, is probably interchain-linked to its counterpart in another molecule, compatible with the existence of dimeric molecules. A minor fraction, with monomeric SP-B but also lacking free thiols, could be due to polypeptides having Cys-57 (instead of Leu in the major form) and hence an additional intrachain bond (Cys-48-Cys-57). Notably, one of the three intrachain bonds common to all SP-B molecules is analogous to one of the disulfide linkages in the kringle structure of complex serine proteases. SP-B and kringles are also similar in size and in positions of half-cystine residues. SP-B and the kringle of coagulation factor XII exhibit 26% residue identity. This structural similarity of SP-B to a binding domain could reflect functional homology, compatible with the notion that SP-B interacts with surfactant anionic phospholipids, which is also in agreement with an SP-B excess of basic residues. Finally, weak similarities between the perform of SP-B and complex serine proteases are also found. This has implications on further possible relationships between kringles, serine proteases, and antiproteases.

Inhibition of mixtures of surfactant lipids and synthetic sequences of surfactant proteins SP-B and SP-C

The respiratory distress syndrome of premature infants is caused by both surfactant deficiency and surfactant inhibition by capillary-alveolar leakage of serum factors. Dispersions of a standard surfactant lipid mixture, with and without various synthetic peptides, modeled on human surfactant proteins SP-B (residues 1-25, 49-66, 1-78) and SP-C (residues 1-10), were evaluated for inhibition by serum and by plasma constituents using a pulsating bubble surfactometer. Inhibition was derived from the changes in surface properties of these mixtures after addition of human serum or plasma constituents. Modified bovine surfactant (TA) containing native SP-B and SP-C was used as a control. In the absence of serum inhibitors, mixtures with synthetic peptides gave results similar to surfactant TA. However, inhibition was more evident in the dispersions with synthetic peptides when compared with surfactant TA. The peptide/phospholipid mixture with the entire sequence of SP-B and the first 10 residues of SP-C were more resistant to inhibition than mixtures with synthetic peptides containing fewer domains. Addition of calcium reduced the inhibitory effects of serum both in mixtures containing synthetic peptides and in surfactant TA. Therefore, synthetic SP-B and SP-C peptides in surfactant lipids, in cooperation with calcium, permit resistance to inhibition by several plasma constituents that probably inactivate surfactant by a variety of different mechanisms.

Immunogenicity of surfactant. I. Human alveolar surfactant

The immunogenicity of lung surfactant derived from amniotic fluid has been well established. We have set out to examine the antigenic similarity of human surfactant to non-human alveolar surfactants currently being used therapeutically in clinical trials with neonatal respiratory distress syndrome. To this end, we raised a series of eight monoclonal antibodies in rats directed to human surfactant (H1 to H8). All antibodies bound human surfactant as measured by ELISA. Four of these monoclonal antibodies bound surfactant components by Western blot analysis: all bound a 9-10-kD species. In addition, one antibody (H2) bound a protein of 16 kD, one (H8) a 6-kD protein, and one (H6) a 30-kD protein. When mixed with surfactant, three antibodies, H4, H7 and H8, profoundly altered surfactant activity in vitro in the pulsating bubble surfactometer. Three other antibodies, H1, H2, and H5 moderately inhibited surfactant's surface activity. We also examined the cross-reactivity of these monoclonal antibodies with bovine (CLSE) and porcine (Curosurf) surfactants. By Western blot analysis, only H6 bound these heterologous surfactants. Other antibodies did so by ELISA. However, functional assays indicated that antibodies H7, H8 and H4 all greatly inhibited CLSE surface activity in vitro. Five antibodies (H1-H4 and H8) inhibited Curosurf function. Thus, human surfactant species, especially low molecular weight species, are highly antigenic. Antibodies to alveolar surfactants may inhibit surfactant function in vitro. As indicated by Western blot and cross-inhibition data, human lower molecular weight surfactants share epitopes with proteins from therapeutically important porcine and bovine surfactants. The potential importance of these findings to treatment of neonatal respiratory distress syndrome with heterologous surfactants is discussed.

The utility of postmortem lung for RNA studies; variability and correlation of the expression of surfactant proteins in human lung

Postmortem human lung tissue was evaluated for its utility in studies of the mRNAs for the surfactant proteins. Data obtained from different analytical procedures indicated that surfactant protein mRNAs are quite stable in these tissues with a half-life of 10 to 12 h. These analyses revealed no major regional differences in the mRNA levels for the surfactant protein A (SP-A) and surfactant protein B (SP-B) although small differences were present in the levels for the surfactant protein C (SP-C). Analysis of adult surgical lung specimens indicated that there is greater individual variation in the mRNA levels for SP-A and SP-B compared to SP-C among individuals. Furthermore, in a given individual the level of SP-A mRNA correlated well with that of SP-B, whereas the level of SP-C mRNA did not correlate with either that of SP-A or SP-B.

Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung

Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term. Four surfactant-associated proteins, SP-A, SP-B, SP-C and SP-D, have recently been characterized. Recognition of their potential importance in the reduction of alveolar surface tension and in endocytosis and reutilization of secreted surfactant by type II cells has stimulated rapid advancement of knowledge concerning the structures of the surfactant proteins and their genes, as well as their developmental and hormonal regulation in fetal lung tissue. The genes encoding SP-A, SP-B and SP-C are expressed in a cell-specific manner and are independently regulated in fetal lung tissue during development. SP-A gene expression occurs exclusively in the type II cell and is initiated after 75% of gestation is complete. In the human fetus, expression of the SP-B and SP-C genes is detectable much earlier in development than SP-A, before the time of appearance of differentiated type II cells. It is apparent from studies using human and rabbit fetal lung in culture that cyclic AMP and glucocorticoids serve important roles in the regulation of SP-A gene expression. While the effects of cyclic AMP are exerted primarily at the level of gene transcription in human fetal lung tissue, glucocorticoids have stimulatory effects on SP-A gene transcription and inhibitory effects on SP-A mRNA stability. In addition, cyclic AMP and glucocorticoids act synergistically to increase SP-A gene transcription in human fetal lung in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Surfactant peptides stimulate uptake of phosphatidylcholine by isolated cells

To determine whether small hydrophobic surfactant peptides (SP-B and SP-C) participate in recycling of pulmonary surfactant phospholipid, we determined the effect of these peptides on transfer of 3H- or 14C-labelled phosphatidylcholine from liposomes to isolated rat alveolar Type II cells and Chinese hamster lung fibroblasts. Both natural and synthetic SP-B and SP-C markedly stimulated phosphatidylcholine transfer to alveolar Type II cells and Chinese hamster lung fibroblasts in a dose- and time-dependent fashion. Effects of the peptides on phospholipid uptake were dose-dependent, but not saturable and occurred at both 4 and 37 degrees C. Uptake of labelled phospholipid into a lamellar body fraction prepared from Type II cells was augmented in the presence of SP-B. Neither SP-B nor SP-C augmented exchange of labelled plasma membrane phosphatidylcholine from isolated Type II cells or enhanced the release of surfactant phospholipid when compared to liposomes without SP-B or SP-C. Addition of native bovine SP-B and SP-C to the phospholipid vesicles perturbed the size and structure of the vesicles as determined by electron microscopy. To determine the structural elements responsible for the effect of the peptides on phospholipid uptake, fragments of SP-B were synthesized by solid-phase protein synthesis and their effects on phospholipid uptake assessed in Type II epithelial cells. SP-B (1-60) stimulated phospholipid uptake 7-fold. A smaller fragment of SP-B (15-60) was less active and the SP-B peptide (40-60) failed to augment phospholipid uptake significantly. Like SP-B and SP-C, surfactant-associated protein (SP-A) enhanced phospholipid uptake by Type II cells. However, SP-A failed to significantly stimulate phosphatidylcholine uptake by Chinese hamster lung fibroblasts. These studies demonstrate the independent activity of surfactant proteins SP-B and SP-C on the uptake of phospholipid by Type II epithelial cells and Chinese hamster lung fibroblasts in vitro.

Isolation and characterization of the cDNA for pulmonary surfactant-associated protein-B (SP-B) in the rabbit

Pulmonary surfactant contains phospholipids including dipalmitoyl-phosphatidylcholine and three surfactant-associated proteins designated SP-A, SP-B and SP-C. A cDNA for rabbit SP-B has been isolated from a fetal (30 days gestation) rabbit lung cDNA library constructed in lambda gt11. The cDNA and deduced amino acid sequences show strong homology with the cDNAs and predicted 40 kDa proproteins for human and canine SP-B. Strong homology is also observed with the amino acid sequences directly determined for the mature 8 kDa bovine and porcine SP-B isolated from lung lavage. SP-B is remarkable for its high cysteine and proline content and for the hydrophobic nature of the organic solvent-soluble, mature protein. In vitro translation of sense but not antisense RNA transcribed from the cDNA led to the production of 40 kDa and 32 kDa proteins. These proteins were immunoprecipitated by an antibody raised against bovine SP-B. Northern blot analysis revealed the mRNA for rabbit SP-B appears in fetal rabbit lung late in gestation and falls slightly in the neonate.

Structure and organization of the gene encoding human pulmonary surfactant proteolipid SP-B

Human pulmonary surfactant proteolipid SP-B arises by proteolytic processing of a 42,000-dalton precursor. The active proteolipid SP-B is one of two small hydrophobic proteins identified in surfactant that impart surface-active properties to surfactant phospholipids. We report the isolation and characterization of complete SP-B cDNA from a human lung cDNA library. The cDNA was used to isolate the gene encoding the SP-B precursor from a lambda EMBL3 library of human embryonic kidney DNA. The entire SP-B gene was sequenced and is approximately 9.5 kb long, with 11 exons and 10 introns including a large 823-nucleotide 3' untranslated exon. The sequence derived from the exons differs from the cDNA sequence at 3 positions out of 2001, only one of which is in the translated region. Direct RNA sequencing indicated that the 5' untranslated region is only 14 nucleotides long. A number of putative regulatory elements were found upstream of the SP-B gene, including a GC box and several putative cAMP and glucocorticoid receptor binding sites. Several Alu repeats and a region of potential Z-DNA formation were found in the introns. Southern blotting of human genomic DNA probed with SP-B cDNA indicated the presence of only one SP-B gene in the human genome, and the gene was localized to chromosome 2.