Here we report that in staurosporine-induced apoptosis of HeLa cells, Bid, a BH3 domain containing protein, translocates from the cytosol to mitochondria. This event is associated with a change in conformation of Bax which leads to the unmasking of its NH2-terminal domain and is accompanied by the release of cytochrome c from mitochondria. A similar finding is reported for cerebellar granule cells undergoing apoptosis induced by serum and potassium deprivation. The Bax-conformational change is prevented by Bcl-2 and Bcl-xL but not by caspase inhibitors. Using isolated mitochondria and various BH3 mutants of Bid, we demonstrate that direct binding of Bid to Bax is a prerequisite for Bax structural change and cytochrome c release. Bcl-xL can inhibit the effect of Bid by interacting directly with Bax. Moreover, using mitochondria from Bax-deficient tumor cell lines, we show that Bid- induced release of cytochrome c is negligible when Bid is added alone, but dramatically increased when Bid and Bax are added together. Taken together, our results suggest that, during certain types of apoptosis, Bid translocates to mitochondria and binds to Bax, leading to a change in conformation of Bax and to cytochrome c release from mitochondria.

Bcl-2 family members either promote or repress programmed cell death. Bax, a death-promoting member, is a pore-forming, mitochondria-associated protein whose mechanism of action is still unknown. During apoptosis, cytochrome C is released from the mitochondria into the cytosol where it binds to APAF-1, a mammalian homologue of Ced-4, and participates in the activation of caspases. The release of cytochrome C has been postulated to be a consequence of the opening of the mitochondrial permeability transition pore (PTP). We now report that Bax is sufficient to trigger the release of cytochrome C from isolated mitochondria. This pathway is distinct from the previously described calcium-inducible, cyclosporin A–sensitive PTP. Rather, the cytochrome C release induced by Bax is facilitated by Mg2+ and cannot be blocked by PTP inhibitors. These results strongly suggest the existence of two distinct mechanisms leading to cytochrome C release: one stimulated by calcium and inhibited by cyclosporin A, the other Bax dependent, Mg2+ sensitive but cyclosporin insensitive.

Bid plays an essential role in Fas-mediated apoptosis of the so-called type II cells. In these cells, following cleavage by caspase 8, the C-terminal fragment of Bid translocates to mitochondria and triggers the release of apoptogenic factors, thereby inducing cell death. Here we report that Bid is phosphorylated by casein kinase I (CKI) and casein kinase II (CKII). Inhibition of CKI and CKII accelerated Fas-mediated apoptosis and Bid cleavage, whereas hyperactivity of the kinases delayed apoptosis. When phosphorylated, Bid was insensitive to caspase 8 cleavage in vitro. Moreover, a mutant of Bid that cannot be phosphorylated was found to be more toxic than wild-type Bid. Together, these data indicate that phosphorylation of Bid represents a new mechanism whereby cells control apoptosis.

Axonal elongation and the transformation of growth cones to synaptic terminals are major steps of brain development and the molecular mechanisms involved form the basis of the correct wiring of the nervous system. The same mechanisms may also contribute to the remodelling of nerve terminals that occurs in the adult brain, as a morphological substrate to memory and learning. We have investigated the function of the nerve terminal protein SNAP-25 (ref. 2) during development. We report here that SNAP-25 is expressed in axonal growth cones during late stages of elongation and that selective inhibition of SNAP-25 expression prevents neurite elongation by rat cortical neurons and PC-12 cells in vitro and by amacrine cells of the developing chick retina in vivo. These results demonstrate that SNAP-25 plays a key role in axonal growth. They also suggest that high levels of SNAP-25 expression in specific areas of the adult brain may contribute to nerve terminal plasticity.

In many areas of science multiple sets of data are collected pertaining to the same system. Examples are food products which are characterized by different sets of variables, bio-processes which are on-line sampled with different instruments, or biological systems of which different genomics measurements are obtained. Data fusion is concerned with analyzing such sets of data simultaneously to arrive at a global view of the system under study. One of the upcoming areas of data fusion is exploring whether the data sets have something in common or not. This gives insight into common and distinct variation in each data set, thereby facilitating understanding the relationships between the data sets. Unfortunately, research on methods to distinguish common and distinct components is fragmented, both in terminology as well as in methods: there is no common ground which hampers comparing methods and understanding their relative merits. This paper provides a unifying framework for this subfield of data fusion by using rigorous arguments from linear algebra. The most frequently used methods for distinguishing common and distinct components are explained in this framework and some practical examples are given of these methods in the areas of (medical) biology and food science.