BESIDES its role in the ATP-mediated degradation of unwanted proteins in the cell, the ubiquitin-proteasome system has also been implicated in a few extra-cellular processes. These include fertilisation in seasquirts, antibacterial activity of chromaffin cells (cells which stimulate production of adrenaline), apoptosis (programmed cell death), homing of haematopoietic stem cells into bone marrow and neural tube development in chick embryo. An Indian research group led by K. Kannan, head of the Biotechnology Department at the Indraprastha University in Delhi, has been involved with the discovery of the last two of these.
Haemotopoietic stem cells are basically the progenitors of all white and red blood cells. They are found in bone marrow. Any defective stem cell can lead to several blood disorders, including leukemia . In 1993, Kannan and his group discovered that ubiquitin molecule acts as a binding agent between the stem cells and the bone marrow. This enables homing of healthy stem cells into bone marrow to cure blood disorders without recourse to radiation and such treatment generally adopted to treat these diseases.
More recently, Kannan's group has shown that there are gross morphological changes in the neural development of the chick embryo after extra-cellular application of uibiquitin. This, he believes, is perhaps owing to some kind of interaction between the extra-cellular ubiquitin and the large population of neural stem cells in the neural tube, as in the case of blood stem cells resulting in the neural development being hampered or delayed. The exact process is not yet clear but, according to Kannan, this has certainly shown that ubiquitin could be a useful probe to study the kinetics of brain development similar to metabolic or enzyme inhibitors in a biochemical pathway.
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