Background: PTEN is targeted by multiple E3 ligases but that does not clearly decipher the rigid control of its level and activity. Results: CHIP interacts with PTEN and promotes its proteasomal degradation. Conclusion: CHIP acts as a bridge between the chaperone system and the degradation machinery for PTEN. Significance: Stabilization of PTEN by targeting CHIP can be a novel therapeutic approach in cancer regulation.

c-Myc is a proto-oncogenic transcription factor and its rapid turnover mediated by the ubiquitin-proteasome system is critical for maintaining normal cellular homeostasis. Multiple ubiquitin ligases have been assigned for c-Myc regulation till date. However, the available data suggest for the possible existence of additional E3 ligase(s). Here, we report a new E3 ligase for c-Myc, the carboxyl terminus of Hsc70-interacting protein or CHIP, which is a chaperone-associated Ubox-containing E3 ligase. In this report, we show that CHIP interacts and ubiquitinates c-Myc, thus targeting it for proteasome-mediated degradation. Overexpression of CHIP could accelerate the turnover rate of c-Myc protein. Conversely, knockdown of CHIP by RNAi stabilizes endogenous c-Myc. The interaction between CHIP and c-Myc depends on the N-terminally located tetratricopeptide repeats of CHIP, which has been implicated as a chaperone-binding motif. Inhibition of Hsp90 chaperone activity by 17-N-allylamino-17-demethoxygeldanamycin reduces c-Myc protein level. We found that the association between CHIP and c-Myc is dependent on the chaperones; particularly Hsp70. CHIP antagonizes the transcriptional activity of c-Myc and decreases the abundance of the transcripts of its target genes. Overall, CHIP-knockdown increases malignant behavior of C6 glioma cells. To the best of our knowledge, this is the first report of c-Myc being regulated by a bona-fide chaperone-associated E3 ligase in HEK293 as well as glioma cells. Because CHIP has been reported earlier to be negatively regulating Akt1, BCR-ABL and hTERT, and now c-Myc, the present study may strengthen the view that CHIP acts as a tumor suppressor.

Strain ST-14, characterized as a member of the genus Cupriavidus, was capable of utilizing 2-and 4-nitrobenzoates individually as sole sources of carbon and energy. Biochemical studies revealed the assimilation of 2-and 4-nitrobenzoates via 3-hydroxyanthranilate and protocatechuate, respectively. Screening of a genomic fosmid library of strain ST-14 constructed in Escherichia coli identified two gene clusters, onb and pob-pca, to be responsible for the complete degradation of 2-nitrobenzoate and protocatechuate, respectively. Additionally, a gene segment (pnb) harboring the genes for the conversion of 4-nitrobenzoate to protocatechuate was unveiled by transposome mutagenesis. Reverse transcription-PCR analysis showed the polycistronic nature of the gene clusters, and their importance in the degradation of 2-and 4-nitrobenzoates was ascertained by gene knockout analysis. Cloning and expression of the relevant pathway genes revealed the transformation of 2-nitrobenzoate to 3-hydroxyanthranilate and of 4-nitrobenzoate to protocatechuate. Finally, incorporation of functional 3-nitrobenzoate dioxygenase into strain ST-14 allowed the recombinant strain to utilize 3-nitrobenzoate via the existing protocatechuate metabolic pathway, thereby allowing the degradation of all three isomers of mononitrobenzoate by a single bacterial strain. IMPORTANCEMononitrobenzoates are toxic chemicals largely used for the production of various value-added products and enter the ecosystem through industrial wastes. Bacteria capable of degrading mononitrobenzoates are relatively limited. Unlike other contaminants, these man-made chemicals have entered the environment since the last century, and it is believed that bacteria in nature evolved not quite efficiently to assimilate these compounds; as a consequence, to date, there are only a few reports on the bacterial degradation of one or more isomers of mononitrobenzoate. In the present study, fortunately, we have been able to isolate a Cupriavidus sp. strain capable of assimilating both 2-and 4-nitrobenzoates as the sole carbon source. Results of the biochemical and molecular characterization of catabolic genes responsible for the degradation of mononitrobenzoates led us to manipulate a single enzymatic step, allowing the recombinant host organism to expand its catabolic potential to assimilate 3-nitrobenzoate.

A heavy metal resistant strain, Pseudomonas stutzeri (MTCC 101) has been investigated for its cadmium tolerance properties along with its antibiotic resistance. The organism could tolerate cadmium up to 1,200 μg/mL with LD50 value 700 μg/mL. The gene(s) involved in such high resistance appear(s) to be induced in the presence of the metal. Increasing concentrations of cadmium successively prolonged the lag phase of growth with delayed attainment of the stationary phase. Transmission electron microscope and scanning electron microscope-energy dispersive analysis of X-ray spectroscope analysis showed cadmium adsorption on the bacterial surface with morphological distortion. Atomic absorption spectrometric study corroborated this data, showing highest cadmium accumulation in the cell wall fraction of the bacteria. Additionally, the cell wall fraction showed synthesis of new proteins when grown under metal stress.

Based on the sole information of structural genes of the 2-nitrobenzoate (2NBA) utilizing catabolic gene cluster (onbX1X2FCAR1EHJIGDBX3), 2NBA-sensing bioreporters were constructed by incorporating egfp into the onb gene cluster of Cupriavidus sp. strain ST-14. Incorporation of reporter gene in proximal to the hypothesized promoter region in conjunction with the disruption of the gene encoding inducer-metabolizing enzyme was turned out to be advantageous in reporter gene expression at low inducer concentration. The bioreporter strain was capable of expressing EGFP from the very 1st hour of induction and could detect 2NBA at (sub) nanomolar level exhibiting a strict specificity toward 2NBA, displaying no response to EGFP expression from its meta- and para-isomers as well as from a number of structurally related compounds. The present study is a successful demonstration of the development of a 2NBA-sensing bioreporter with respect to ease of construction, inducer specificity, and sensitivity, without prior knowledge of the associated inducer-responsive promoter-regulator elements. The present approach can be used as a model for the development of bioreporters for other environmental pollutants.

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