academy reseach |
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| 등록일 : 2014-05-22 조회수 : 365 작성자 : welson |
| <div style="display:none">fiogf49gjkf0d</div>Abstract The majority of Mycobacterium tuberculosis (MTB) infections are clinically latent, characterized by drug tolerance and little or no bacterial replication. Low oxygen tension is a major host factor inducing bacteriostasis, but the molecular mechanisms driving oxygen-dependent replication are poorly understood. Here, we tested the role of serine/threonine phosphorylation in the MTB response to altered oxygen status, using an in vitro model of latency(hypoxia) and reactivation (reaeration). Broad kinase inhibition compromised survival of Mtb in reaeration. Activity-based protein profiling and genetic mutation identified PknB as the kinase critical for surviving hypoxia. Mtb replication was highly sensitive to changes in PknB levels in aerated culture, and even more so in hypoxia. A mutant overexpressing PknB specifically in hypoxia showed a 10-fold loss in viability and gross morphological defects in low oxygen conditions. In contrast, chemically reducing PknB activity during hypoxia specifically compromised resumption of growth during reaeration. These data support a model in which PknB activity is reduced to achieve bacteriostasis, and elevated when replication resumes. Together, these data show that phosphosignaling controls replicative transitions associated with latency and reactivation, that PknB is a major regulator of these transitions, and that PknB could provide a highly vulnerable therapeutic target at every step of the Mtb life cycle—active disease, latency, and reactivation. Author Summary Exposure to Mycobacterium tuberculosis (MTB) can result in a latent form of tuberculosis (TB) infection, which can then reactivate and progress to active disease. With 1.8 billion infected persons and no tools to predict who will proceed to active disease, latency and reactivation are among the major challenges of TB treatment and control. Oxygen is one of the environmental triggers affecting the balance between latency and reactivation. Normal oxygen levels promote exponential bacterial growth in culture, but low oxygen levels (hypoxia) inhibit such growth, inducing reversible bacteriostasis. How Mtb regulates this oxygen-dependent replication switch, however, is still unknown. Here we tested the role of serine/threonine protein kinases—signaling molecules that transmit environmental cues into cellular responses—in this process. We found that kinase inhibition led to a bacterial survival defect and we specifically identified the PknB kinase as a critical regulator of the oxygen-dependent replication switch. Mtb growth was sensitive to elevated levels of PknB and this sensitivity increased in hypoxia. Inhibition of PknB activity led to defects in Mtb replication. These data show that signaling through PknB modulates the growth and replication state of Mtb in response to oxygen, suggesting that PknB could be a drug target by which to control both the active replicating and latent nonreplicating forms of Mtb. |
