Replication rates of Mycobacterium tuberculosis in human macrophages do not correlate with mycobacterial antibiotic susceptibility

The standard treatment of tuberculosis (TB) takes six to nine months to complete and this lengthy therapy contributes to the emergence of drug-resistant TB. TB is caused by Mycobacterium tuberculosis (Mtb) and the ability of this bacterium to switch to a dormant phenotype has been suggested to be responsible for the slow clearance during treatment. A recent study showed that the replication rate of a non-virulent mycobacterium, Mycobacterium smegmatis, did not correlate with antibiotic susceptibility. However, the question whether this observation also holds true for Mtb remains unanswered. Here, in order to mimic physiological conditions of TB infection, we established a protocol based on long-term infection of primary human macrophages, featuring Mtb replicating at different rates inside the cells. During conditions that restricted Mtb replication, the bacterial phenotype was associated with reduced acid-fastness. However, these phenotypically altered bacteria were as sensitive to isoniazid, pyrazinamide and ethambutol as intracellularly replicating Mtb. In support of the recent findings with M. smegmatis, we conclude that replication rates of Mtb do not correlate with antibiotic tolerance.

Abstract 4897: Genetic variants and expression of AEG-1 in relation to clinical outcome and radiotherapy response in colorectal cancer patients and cell lines

Background: Colorectal cancer (CRC) is the third most common cancer in men and the second in woman worldwide. The therapy of CRC has been critically improved during the past two decades, but the treatment response varies significantly between different treatments and patients. Therefore it is of need to search for biomarkers for more suitable prognosis and treatment. The aim of this study was to investigate genetic variants of the astrocyte elevated gene-1 (AEG-1), its expression in CRC patient samples and colon cancer cell lines and the potential correlation to clinicopathological variables and treatment response.

Materials and Methods: We analysed genetic variants and the mRNA and protein expression of AEG-1 in 593 CRC patient samples by direct Sanger sequencing, qPCR and immunohistochemistry. Of the patients, 158 rectal cancer patients were enrolled in the Swedish clinical trial of preoperative radiotherapy (RT). AEG-1 expression in response to γ-irradiation was analysed by Western blot in 5 colon cancer cell lines. We inhibited the AEG-1 expression by siRNA in the cell lines, and their survival was analysed after γ-irradiation.

Results: By direct sequencing we found 29 variants, of which 12 were novel. Six of the variants were exonic and 23 intronic. The variant c.1353G>A, rs2331652 was found only in 4 samples and the variant c.1679-6 T>C in only one sample. In the cell lines KM12C, KM12SM and KM12L4a we found a deletion in exon 4 (c.595_598delAGAG). AEG-1 mRNA and protein expression revealed a significant increased AEG-1 expression in the primary tumors and metastases compared to the normal mucosa in all patient cohorts (p<0.006) and on the mRNA level a higher expression in tumors located in the rectum compared to tumors in the colon (p=0.047). In the rectal cancer patients from the Swedish trail of preoperative

RT, a high AEG-1 expression correlated with a higher risk of distant recurrence and disease free survival (p=0.001 respectively) independently of the tumor stage, only in patients receiving preoperative RT. AEG-1 knock-down in the radioresistant cell lines KM12L4a, SW480 and SW620 resulted in reduction of the survival after radiation, but not in the radiosensitive cell lines KM12C and HCT116. The AEG-1 expression was up-regulated shortly after 2 Gy γ-radiation in KM12C, KM12L4a and SW480, but not in SW620 and HCT116.

Conclusion: We found several novel AEG-1 variants. The AEG-1 expression at the mRNA and/or protein level was up-regulated in the primary tumour and metastases compared to the normal mucosa. Furthermore we showed for the first time that the AEG-1 expression is an independent prognostic factor for distant recurrence and disease-free survival in rectal cancer patients after treatment with preoperative RT. The cell line studies suggest AEG-1 as a promising radiosensitizing target for rectal cancer.

Citation Format: Sebastian Gnosa, Veronika Patcha Brodin, Ivana Ticha, Gunnar Adell, Gunnar Arbman, Hong Zhang, Xiao-Feng Sun. Genetic variants and expression of AEG-1 in relation to clinical outcome and radiotherapy response in colorectal cancer patients and cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4897. doi:10.1158/1538-7445.AM2014-4897

AEG-1 expression is an independent prognostic factor in rectal cancer patients with preoperative radiotherapy: a study in a Swedish clinical trial

Background:

Preoperative radiotherapy (RT) is widely used to downstage rectal tumours, but the rate of recurrence varies significantly. Therefore, new biomarkers are needed for better treatment and prognosis. It has been shown that astrocyte elevated gene-1 (AEG-1) is a key mediator of migration, invasion, and treatment resistance. Our aim was to analyse the AEG-1 expression in relation to RT in rectal cancer patients and to test its radiosensitising properties.

Methods:

The AEG-1 expression was examined by immunohistochemistry in 158 patients from the Swedish clinical trial of RT. Furthermore, we inhibited the AEG-1 expression by siRNA in five colon cancer cell lines and measured the survival after irradiation by colony-forming assay.

Results:

The AEG-1 expression was increased in the primary tumours compared with the normal mucosa independently of the RT (P<0.01). High AEG-1 expression in the primary tumour of the patients treated with RT correlated independently with higher risk of distant recurrence (P=0.009) and worse disease-free survival (P=0.007). Downregulation of AEG-1 revealed a decreased survival after radiation in radioresistant colon cancer cell lines.

Conclusions:

The AEG-1 expression was independently related to distant recurrence and disease-free survival in rectal cancer patients with RT and could therefore be a marker to discriminate patients for distant relapse.

Common genetic variations in the NALP3 inflammasome are associated with delayed apoptosis of human neutrophils

Background

Neutrophils are key-players in the innate host defense and their programmed cell death and removal are essential for efficient resolution of inflammation. These cells recognize a variety of pathogens, and the NOD-like receptors (NLRs) have been suggested as intracellular sensors of microbial components and cell injury/stress. Some NLR will upon activation form multi-protein complexes termed inflammasomes that result in IL-1β production. NLR mutations are associated with auto-inflammatory syndromes, and our previous data propose NLRP3 (Q705K)/CARD-8 (C10X) polymorphisms to contribute to increased risk and severity of inflammatory disease by acting as genetic susceptibility factors. These gene products are components of the NALP3 inflammasome, and approximately 6.5% of the Swedish population are heterozygote carriers of these combined gene variants. Since patients carrying the Q705K/C10X polymorphisms display leukocytosis, the aim of the present study was to find out whether the inflammatory phenotype was related to dysfunctional apoptosis and impaired clearance of neutrophils by macrophages.

Methods and Findings

Patients carrying the Q705K/C10X polymorphisms displayed significantly delayed spontaneous as well as microbe-induced apoptosis compared to matched controls. Western blotting revealed increased levels and phosphorylation of Akt and Mcl-1 in the patients' neutrophils. In contrast to macrophages from healthy controls, macrophages from the patients produced lower amounts of TNF; suggesting impaired macrophage clearance response.

Conclusions

The Q705K/C10X polymorphisms are associated with delayed apoptosis of neutrophils. These findings are explained by altered involvement of different regulators of apoptosis, resulting in an anti-apoptotic profile. Moreover, the macrophage response to ingestion of microbe-induced apoptotic neutrophils is altered in the patients. Taken together, the patients display impaired turnover and clearance of apoptotic neutrophils, pointing towards a dysregulated innate immune response that influences the resolution of inflammation. The future challenge is to understand how microbes affect the activation of inflammasomes, and why this interaction will develop into severe inflammatory disease in certain individuals.

Inactivation of Cdc42 Is Necessary for Depolymerization of Phagosomal F-Actin and Subsequent Phagosomal Maturation

Phagocytosis is a complex process involving the activation of various signaling pathways, such as the Rho GTPases, and the subsequent reorganization of the actin cytoskeleton. In neutrophils, Rac and Cdc42 are activated during phagocytosis but less is known about the involvement of these GTPases during the different stages of the phagocytic process. The aim of this study was to elucidate the role of Cdc42 in phagocytosis and the subsequent phagosomal maturation. Using a TAT-based protein transduction technique, we introduced dominant negative and constitutively active forms of Cdc42 into neutrophil-like HL60 (human leukemia) cells that were allowed to phagocytose IgG-opsonized yeast particles. Staining of cellular F-actin in cells transduced with constitutively active Cdc42 revealed that the activation of Cdc42 induced sustained accumulation of periphagosomal actin. Moreover, the fusion of azurophilic granules with the phagosomal membrane was prevented by the accumulated F-actin. In contrast, introducing dominant negative Cdc42 impaired the translocation per se of azurophilic granules to the periphagosomal area. These results show that efficient phagosomal maturation and the subsequent eradication of ingested microbes in human neutrophils is dependent on a strictly regulated Cdc42. To induce granule translocation, Cdc42 must be in its active state but has to be inactivated to allow depolymerization of the F-actin cage around the phagosome, a process essential for phagolysosome formation.