Until birth, binary IGFBP/IGF complexes of 50 kD predominate in serum, with IGFBP2 being
the most frequently occurring IGFBP moiety. In juvenile and adult mammals, however, 80% to 85% of serum IGFs are found in a ternary
complex of 150 kD composed of 1 molecule each of IGF, IGFBP3, and a protein that is found only in serum, the acid-labile
subunit (ALS). ALS migrates at an apparent molecular mass of 84-86 kD. ALS cDNAs predict signal peptide and mature
protein of 23 and 580 amino acids in the rat, and 27 and 578 amino acids in humans. ALS retains the IGFBP3/IGF complexes
in the vascular compartment and extends the half life of IGFs in the circulation. Synthesis of ALS occurs mainly in liver after
birth and is stimulated by growth hormone.
NCBI Summary:
The protein encoded by this gene is a serum protein that binds insulin-like growth factors, increasing their half-life and their vascular localization. Production of the encoded protein, which contains twenty leucine-rich repeats, is stimulated by growth hormone. Defects in this gene are a cause of acid-labile subunit deficiency, which maifests itself in a delayed and slow puberty. Three transcript variants encoding two different isoforms have been found for this gene. [provided by RefSeq, Mar 2009]
Wandji SA, et al 2000 reported that porcine ovarian cells express messenger ribonucleic acids for the acid-labile subunit (ALS) and insulin-like
growth factor binding protein-3 during follicular and luteal phases of the estrous cycle. These transcripts were colocalized with aromatase mRNA, a marker
of healthy granulosa cells. IGFBP-3 mRNA was equally expressed in granulosa cells of all growing follicles. In contrast,
granulosa cell ALS mRNA levels were higher in preantral and small antral follicles than in large antral follicles.
In thecal cells, expression of mRNA for IGFBP-3, ALS and cyclin D1 (a marker of cell proliferation) was restricted to
healthy (aromatase-expressing) follicles. In those follicles, thecal expression of IGFBP-3 mRNA was low or absent in
preantral follicles but increased (P < 0.05) in antral follicles. Thecal cell ALS transcripts peaked in small antral follicles (P
< 0.05) and then declined. In granulosa cells of atretic follicles, transcripts for aromatase were greatly reduced, whereas
IGFBP-3 mRNA levels remained high. In contrast, ALS transcript levels were greatly reduced in both granulosa and thecal cells of atretic follicles. After ovulation, IGFBP-3 mRNA was moderately expressed in granulosa
luteins but strongly detected in a few theca-derived cells and in vascular endothelial cells. This study demonstrates that
follicular fluid IGFBP-3 and ALS, like the IGFs, originate (at least in part) from the ovary. The ability of follicular cells to
synthesize, assemble, and store all components of the ternary complex may be critical in determining the bioavailability of
follicular IGF-I and -II.
Expression regulated by
Comment
Ovarian localization
Granulosa, Theca, Luteal cells
Comment
Wandji SA, et al 2000 reported that
porcine ovarian cells express messenger ribonucleic acids for
the acid-labile subunit (ALS) and insulin-like growth factor binding
protein-3 during follicular and luteal phases of the estrous
cycle.
IGFBP-3 mRNA was equally expressed
in granulosa cells of all growing porcine follicles. In contrast, granulosa cell ALS
mRNA levels were higher (P < 0.05) in preantral and small antral follicles
than in large antral follicles. In thecal cells, expression of mRNA for
IGFBP-3, ALS and cyclin D1 (a marker of cell proliferation) was restricted to
healthy (aromatase- expressing) follicles.
Thecal cell ALS transcripts peaked
in small antral follicles (P < 0.05) and then declined. In granulosa cells of
atretic follicles, transcripts for aromatase were greatly reduced, whereas
IGFBP-3 mRNA levels remained high. In contrast, ALS transcript levels were
greatly reduced in both granulosa (P < 0.05) and thecal cells (P < 0.001) of
atretic follicles. This study demonstrates that follicular fluid
IGFBP-3 and ALS, like the IGFs, originate (at least in part) from the ovary.Lee CY, et al 2001 reported low levels of ALS mRNA were also present in adult muscle, spleen,
ovary and uterus.