Secretion of hepatoma-derived growth factor is regulated by N-terminal processing

Hepatoma-derived growth factor (HDGF) was first purified as a growth factor secreted by hepatoma cells. It promotes angiogenesis and has been related to tumorigenesis. To date, little is known about the molecular mechanisms of HDGF functions and especially its routes or regulation of secretion. Here we show that secretion of HDGF requires the N-terminal 10 amino acids and that this peptide can mediate secretion of other proteins, such as enhanced green fluorescent protein, if fused to their N-terminus. Our results further demonstrate that cysteine residues at positions 12 and 108 are linked via an intramolecular disulfide bridge. Surprisingly, phosphorylation of serine 165 in the C-terminal part of HDGF plays a critical role in the secretion process. If this serine is replaced by alanine, the N-terminus is truncated, the intramolecular disulfide bridge is not formed and the protein is not secreted. In summary, these observations provide a model of how phosphorylation, a disulfide bridge and proteolytic cleavage are involved in HDGF secretion.     

Seasonal variation in antioxidant enzymes and the sprouting response of Gmelina arborea Roxb. nodal sectors cultured in vitro

Nodal sector explants of Gmelina arborea Roxb. showed seasonal variation in the sprouting of axillary buds in vitro. Explants from mature trees showed only 20% sprouting in summer, while those from seedlings and young trees showed over 85% sprouting in this season. In winter, there was a significant decrease in the sprouting response of explants from young and mature trees but not in that of seedling explants. We have attempted to correlate the sprouting response of the explants with their antioxidant status. Activities of three enzymes, namely ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase which form a part of the antioxidant defense system of plants, were studied in the excised nodal sectors before and after placing them on culture medium. Prior to culture, higher activities of ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase were observed during winter than during summer. During the culture period, ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase showed variation depending on the season in which the explants were isolated, and the age of the donor. Axillary bud sprouting in vitro appeared to depend more on the physiological state of the donor, than on the oxidative stress generated during culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Catecholamine response of children in a naturally occurring stressor situation

The present study examined the response of children to a stressor condition. Urine samples were collected from 38 children between ages 10 and 12 preceding a class presentation and again one week later, when no unusual event was occurring. Cognitive tasks and a state anxiety inventory were administered on both occasions. Personality and stressor situation inventories (hypothesized antecedent factors) were completed. Bidirectional changes in catecholamine levels were demonstrated (adrenalin: 55% of the children showed an increase, 29% a decrease; noradrenalin: 47% increase, 40% decrease; 3-methoxy-4-hydroxyphenethylene glycol: 40% increase, 42% decrease). Distinct differences in gender distribution and cognitive performance were demonstrated for the increase and decrease subgroups. It was suggested that both increases and decreases in catecholamine levels represent responses to the stressor situation, with an increase representing an adaptive response and a decrease representing a less adaptive response.