A digital microfluidic method for multiplexed cell-based apoptosis assays

Digital microfluidics (DMF), a fluid-handling technique in which picolitre-microlitre droplets are manipulated electrostatically on an array of electrodes, has recently become popular for applications in chemistry and biology. DMF devices are reconfigurable, have no moving parts, and are compatible with conventional high-throughput screening infrastructure (e.g., multiwell plate readers). For these and other reasons, digital microfluidics has been touted as being a potentially useful new tool for applications in multiplexed screening. Here, we introduce the first digital microfluidic platform used to implement parallel-scale cell-based assays. A fluorogenic apoptosis assay for caspase-3 activity was chosen as a model system because of the popularity of apoptosis as a target for anti-cancer drug discovery research. Dose-response profiles of caspase-3 activity as a function of staurosporine concentration were generated using both the digital microfluidic method and conventional techniques (i.e., pipetting, aspiration, and 96-well plates.) As expected, the digital microfluidic method had a 33-fold reduction in reagent consumption relative to the conventional technique. Although both types of methods used the same detector (a benchtop multiwell plate reader), the data generated by the digital microfluidic method had lower detection limits and greater dynamic range because apoptotic cells were much less likely to de-laminate when exposed to droplet manipulation by DMF relative to pipetting/aspiration in multiwell plates. We propose that the techniques described here represent an important milestone in the development of digital microfluidics as a useful tool for parallel cell-based screening and other applications.

Molecular characterization of hsp90 isoforms in colorectal cancer cells and its association with tumour progression

A key role of hsp90 in the activity of various oncogenic proteins and pathways is currently of intense interest. To clarify the molecular basis of biological behaviour of colorectal cancers we analysed the expression characteristics of hsp90 in cytosolic, nuclear and plasma membranous fractions of cancer cells. As determined by Western blot assay all hsp90 isoforms studied, alpha (84 kDa), beta (86 kDa) and hsp90N (75 kDa), were up-regulated and differentially expressed in various stages of colorectal carcinoma. The inducible hsp90alpha isoform is a component of invasive phenotype of cancer cells thus pointing to the importance of hsp90alpha for metastasis generation. The expression of hsp90beta is definitely higher in poorly-differentiated carcinomas than in well-differentiated cancers, suggesting an involvement of hsp90beta in the inhibition of cancer cell differentiation. Especially, the expression of cytosolic hsp90N isoform in malignant cells points to the possibility that induction or overexpression of hsp90N might be causally related to tumour formation. Hsp90N is the plasma-membrane-associated protein in poorly-differentiated colorectal cancers with metastasis. This suggests that the expression of hsp90N is elevated with progressive dedifferentiation often associated with advanced cancer stages. Hsp90 was exclusively localized in the invasive front in a majority of metastatic cancers as visualized by immunohistochemical study. Consistent with these facts, the frequent expression of hsp90alpha and hsp90N on the surface of colorectal cancer cells may enable hsp90 to act as a mediator of metastasis generation. The above results indicate more complex roles for hsp90 in colorectal tumourigenesis. In this way, the hsp90 would be at the crossroads of both signalling and cell migration events.

C/EBPalpha and C/EBPbeta are persistently associated with the rat liver nuclear matrix throughout development and the acute phase response

The partitioning of C/EBPalpha and C/EBPbeta on the nuclear matrix structure was examined during the different transcriptional activities accompanying liver development and the acute phase (AP) response. The presence of C/EBPalpha and C/EBPbeta was established on the nuclear matrix. Their relative concentrations on the matrix always reflected the developmental stage- and AP-related fluctuations observed in the nuclear extract. Thus, they progressively increased as development proceeded, whereas during the AP response, C/EBPalpha decreased and C/EBPbeta increased. In addition, the levels of both transcription factors were always notably higher in the nuclear matrix than in the extracts. We conclude that the observed changes and overall enrichment of the nuclear matrix with regulatory proteins is a reflection of the importance of such interactions for the in vivo functioning of C/EBP proteins.