Cold Shock Response of the UspA1 Outer Membrane Adhesin of Moraxella catarrhalis

Abstract

Colonization of the human nasopharynx exposes Moraxella catarrhalis, a common cause of otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults, to sudden downshifts in temperature, occurring when the host breathes cold air. We investigated whether in vitro cold shock influences the expressions of the outer membrane adhesins UspA1 and hemagglutinin, which are considered virulence factors, and of an M. catarrhalis homolog of recA, a housekeeping gene, which in Escherichia coli is induced by cold shock. Quantitative real-time reverse transcriptase PCR was used for measuring mRNA copy number. A screening experiment revealed that a cold shock at 26°C maximally induced the copy number of uspA1. In comparison with 37°C conditions, a 1-hour cold shock at 26°C increased copy numbers of uspA1 and recA by 2.5-fold (11.2 ؎ 1.8 versus 4.5 ؎ 0.8 copies/CFU) and 2.7-fold (0.30 ؎ 0.10 versus 0.11 ؎ 0.06), respectively, but did not induce transcription of hag. Exposure to 26°C increased surface expression of UspA1, as assessed by fluorescence-activated cell sorter analysis, and resulted in a significant increase in adherence of strain O35E to Chang human conjunctival cells (97.1% ؎ 2.0% versus 48.3% ؎ 9.2% at 37°C; P ‫؍‬ 0.01). Cold shock induction of uspA1 and recA was detected in strains belonging to either phylogenetic subpopulation of M. catarrhalis (16S rRNA types 1 and 2/3) and was most pronounced in type 2/3 strains (4-to 25-fold for uspA1), which do not express detectable amounts of UspA1 protein at 37°C. These data indicate that cold shock at a physiologically relevant temperature of 26°C induces the expression of at least one virulence factor (UspA1). To our knowledge, no similar data are available for other nasopharyngeal pathogens.Moraxella catarrhalis is exclusively a pathogen of primates. No other host organisms or environmental reservoirs have been identified (7,35). Intimate adaptation to the primate host is illustrated by, for instance, the specificity of M. catarrhalis transferrin-binding proteins for transferrin of primate origin (14) and by the organism's capacity to grow with iron-loaded human transferrin or lactoferrin as the sole source of iron (9).M. catarrhalis colonizes the mucosal surface of the nasopharynx and causes upper and lower respiratory tract infections (28,35). Colonization rates exceeding 50% in infants and young children (12, 39) indicate efficient person-to-person transmission and successful adaptation to environmental conditions found in the upper respiratory tract. Temperature is one of the key environmental variables with which microorganisms are confronted. Temperature determines molecular dynamics and diffusion rates, enzyme kinetics, and secondary structures of macromolecules and is thus a fundamental determinant of cellular function (40). Despite its close association with a single colonization site in a single warm-blooded host, M. catarrhalis is exposed to brisk fluctuations of temperature. Breathing cold air reduces nasopharyngeal temperature...

Molecular Aspects ofMoraxella catarrhalisPathogenesis

“…Interestingly, expression of uspA1 and uspA2 has been found to be associated with different 16S rRNA subtypes, as strains with normal uspA1 and uspA2 expression levels are of 16S rRNA type 1, and strains with negligible expression are predominantly of 16S rRNA types 2 and 3 (95). Additionally, the expression of uspA1 could be induced by cold shock (26°C) in strains of all three 16S rRNA subtypes (63), although upregulation was most prominent in strains that normally exhibited negligible uspA1 expression, namely, those of 16S rRNA subtypes 2 and 3. Whether this cold shock-induced increase in uspA1 expression is mediated by variation in the poly(G) tract…”

“…However, cold shock could lead to the accumulation of specific mRNAs due to transcriptional and posttranscriptional responses in a manner similar to that observed in Streptococcus pyogenes, in which 9% of the genes have been found to be differentially expressed upon cold shock (140). Cold shock-induced upregulation of uspA1 could be beneficial for survival in the nasopharynx, especially the nose, which experiences regular temperature fluctuations and is generally cooler than the rest of the body (63). One of the receptors on human epithelial cells to which UspA1 binds has been found to be the CEACAM1 (67,68).…”

Expression of the Oligopeptide Permease Operon of Moraxella catarrhalis Is Regulated by Temperature and Nutrient Availability

“…The temperature of the human nasopharynx is variable, with measurements ranging from 37°C to 26°C (2,(17)(18)(19)(20)(21)(22). Temperature has an important impact on virulence factors and transcriptional regulation in M. catarrhalis (23)(24)(25). When cultures were grown at 26°C, the transcript levels of all of the opp genes were significantly elevated compared to transcript levels at 37°C (Fig.…”

“…Exposure to cold shock at 26°C has an important impact on virulence factors and transcriptional regulation in M. catarrhalis (23)(24)(25).…”

Influence of thespxBGene on Competence inStreptococcus pneumoniae

“…Quantitation of absolute mRNA copy numbers by real-time RT-PCR was performed by using a standard curve generated based on in vitro-transcribed RNA (cRNA) as previously described (12,16). For the in vitro transcription of the spxB, comC, and recA genes, the following primers were used: spxB_F1_T7 (5Ј-TAATACGA CTCACTATAGGGAGAGTGGAATAGTAAAAATTTGGAGAACG-3Ј) and spxB_Bac1 (5Ј-CGATCTTTTAAAGTTCTGCTCTATG-3Ј), comC_Start1_T7 (5Ј-TAATACGACTCACTATAGGGAGAAATCTTTCTGTCAGTTTTGGTC G-3Ј) and comC_End1 (5Ј-GTCCCAAATCCAAATAAATCCAT-3Ј), and recA_Start1_T7 (5Ј-TAATACGACTCACTATAGGGAGAGTACGTCACAT TGCGGTTATGC-3Ј) and recA_End1 (5Ј-GAATCAAAAATCGAAAAAGTA GCG-3Ј) (the T7 promoter is underlined).…”