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Regarding the
http://en.wikipedia.org/wiki/Heterotrimeric_g_protein
heterotrimeric G protein wikipedia says: "Regulators of
G-protein Signaling
(see GTPase)". "Regulatory GTPases Regulatory GTPases,
also called the
GTPase superfamily, are GTPases used for regulation of other
biochemical
processes. Most prominent among the regulatory GTPases are
the G proteins."
It appeared from the free to all full text (1) paper said
that one of the
regulator of G proteins (Rgs) called Rgs16 may suppress
inflammation, as
does CR. It also appears that this may be true, based on
(2) paper, in which fasting and its associated weight
reduction (therefore, probably CR) is the unique Rgs that is
affected by our biological rhythm, or clock. Rgs 16 may be
involved in eating/metabolism.

1. Lippert E, Yowe DL, Gonzalo JA, Justice JP, Webster JM,
Fedyk ER, Hodge
M, Miller C, Gutierrez-Ramos JC, Borrego F, Keane-Myers A,
Druey KM.
Role of regulator of G protein signaling 16 in
inflammation-induced T
lymphocyte migration and activation.
J Immunol. 2003 Aug 1;171(3):1542-55.
PMID: 12874248

2. Huang J, Pashkov V, Kurrasch DM, Yu K, Gold SJ, Wilkie TM.
Feeding and fasting controls liver expression of a regulator
of G protein
signaling (Rgs16) in periportal hepatocytes.
Comp Hepatol. 2006 Nov 23;5(1):8 [Epub ahead of print]
PMID: 17123436

ABSTRACT: BACKGROUND: Heterotrimeric G protein signaling in
liver helps
maintain carbohydrate and lipid homeostasis. G protein
signaling is
activated by binding of extracellular ligands to G protein
coupled receptors
and inhibited inside cells by regulators of G protein
signaling (RGS)
proteins. RGS proteins are GTPase activating proteins, and
thereby regulate
Gi and/or Gq class G proteins. RGS gene expression can be
induced by the
ligands they feedback regulate, and RGS gene expression can
be used to mark
tissues and cell-types when and where Gi/q signaling occurs. We
characterized the expression of mouse RGS genes in liver
during fasting and
refeeding to identify novel signaling pathways controlling
changes in liver
metabolism. RESULTS: Rgs16 is the only RGS gene that is
diurnally regulated
in liver of ad libitum fed mice. Rgs16 transcription, mRNA
and protein are
up regulated during fasting and rapidly down regulated after
refeeding.
Rgs16 is expressed in periportal hepatocytes, the
oxygen-rich zone of the
liver where lipolysis and gluconeogenesis predominates.
Restricting feeding
to 4 hr of the light phase entrained Rgs16 expression in
liver but did not
affect circadian regulation of Rgs16 expression in the
suprachiasmatic
nuclei (SCN). CONCLUSIONS: Rgs16 is one of a subset of genes
that is
circadian regulated both in SCN and liver. Rgs16 mRNA
expression in liver
responds rapidly to changes in feeding schedule, coincident
with key
transcription factors controlling the circadian clock. Rgs16
expression can
be used as a marker to identify and investigate novel
G-protein mediated
metabolic and circadian pathways, in specific zones within
the liver.

... Results
Diurnal regulation of Rgs16 mRNA in liver
The diurnal expression of Rgs16 was characterized in liver
of C57BL/6 female
mice (pair caged) with free access to food and water under
conditions of 12
hr light/dark, and sacrificed every 4 hrs at nine time
points throughout a
36-hour period (Fig 1A). Interestingly, Rgs16 mRNA
accumulated toward the
end of the light phase, just prior to when animals begin
feeding. Rgs16 mRNA
returned to basal levels during the dark phase, presumably
after feeding,
and remained at basal levels until the middle of the next
light phase. Rgs16
mRNA levels were always up regulated by eight hr into the
light phase
(Zeitgeber time 8 hr; ZT8) but some variation in expression
was observed at
ZT12 (Fig 1A, compare ZT12 Day 1 vs Day 2). About half of
the ad libitum fed
mice we assayed at ZT12 expressed high levels (similar to
ZT8) of Rgs16 mRNA
in liver (n > 40), whereas the mice with lower expression
probably began
feeding prior to lights out (see below). The diurnal rhythm
in Rgs16
expression was observed in male and female mice and rats
ranging in age from
four weeks to more than one year. Diurnal oscillation in
mRNA expression in
liver was not observed for any of the other 19 RGS genes
expressed in mice
[32].

Rgs16 is one of a small subset of genes that is diurnally
regulated in both
liver and the hypothalamic suprachiasmatic nuclei (SCN),
site of the central
circadian pacemaker [33, 34]. We showed by in situ
hybridization that Rgs16
mRNA is expressed in the SCN of C57BL/6 female mice in our
colony in the
same temporal pattern as previously reported (Fig. 1B;
[35]). Furthermore,
this temporal pattern of Rgs16 expression in the SCN is
maintained in ad
libitum fed mice housed in constant darkness (CD) for two
days prior to
sacrifice on the third day; expression is elevated at 6 hr
into the
presumptive light phase (CD6) and declines to basal levels
by 2 hr into the
presumptive dark phase (CD14; Fig. 1C). Thus, Rgs16
expression in the SCN
appears to be entrained similarly to other circadian
regulated genes [35,
36].

Regulation of Rgs16 by fasting and refeeding
To determine whether Rgs16 mRNA expression in liver was
upregulated in
anticipation of a meal, but returned to basal levels after
feeding, we
examined the effect of withholding food on Rgs16 mRNA levels
and refeeding
at different times in the light cycle. Fasting mice for
various intervals
caused an increase in Rgs16 mRNA expression through the
early-middle hours
of the first dark phase (Fig. 2A, lanes 1,4). The induction
of Rgs16 mRNA
expression early in the fasting period was consistently
observed in separate
groups of female mice fasted from ZT4; but expression levels
began to vary
as the mice were fasted through the dark phase until ZT12 of
the following
day (Fig. 2A, lanes 6-7; Fig. 2B; solid line). By contrast,
phosphoenolpyruvate carboxykinase (PEPCK) expression never
declined at any
time in any of those fasted mice (Fig. 2B; dashed line). In
all cases,
Rgs16 (and PEPCK) mRNA expression returned to basal levels
within four hours
of providing chow ad libitum (Fig 2A, conditions 3,5,8) or
within 90 min
after gavage of a complete liquid diet (Fig. 2C). Gavage
with water did not
affect Rgs16 expression, suggesting that stomach dilation or
gastrointestinal motility are not factors regulating liver
Rgs16 expression
during fasting and refeeding.

Rgs16 mRNA in periportal hepatocytes
Metabolic functions of the liver are distributed between
zones of
hepatocytes organized within acini [37]. Lypolysis and
gluconeogenesis occur
preferentially in periportal hepatocytes, whereas glycolysis
and lipogenesis
occur preferentially in hepatocytes surrounding the central
vein [37]. The
hepatic cell types that expressed Rgs16 mRNA were identified
by in situ
hybridization. Interestingly, Rgs16 expression in fasted
mice was localized
to periportal hepatocytes that surround the portal triad,
consisting of a
portal vein, a hepatic artery, and a bile duct (Fig. 3A,B;
same condition as
Fig 2 condition 4). Rgs16 expression remained tightly
restricted to
periportal hepatocytes even after a 24 hr fast. By contrast,
PEPCK mRNA was
expressed in hepatocytes throughout the liver of fasted
mice, although it
was most abundant in periportal hepatocytes (Fig 3D).
Periportal expression
of Rgs16 and PEPCK was confirmed by histological
examination. Consistent
with previous Northern analyses, Rgs16 mRNA expression was
not detected by
in situ hybridization in liver of fed mice (Fig 3C; same
conditions as Fig
2, lane 2). In additional control experiments, sense probes
of Rgs16 and
PEPCK did not hybridize to adjacent sections (data not
shown). The
restricted pattern of Rgs16 expression to periportal
hepatocytes suggests
that Rgs16 may regulate lipolysis and/or gluconeogensis in
liver.

Restricted feeding shifts circadian expression of Rgs16 in
liver but not SCN
Regulation of Rgs16 by fasting and refeeding suggested that
restricted
feeding (RF), during 4 hours of the light phase (ZT5-ZT9),
might shift Rgs16
expression in liver along with transcription factors that
control the
circadian clock in peripheral tissues [35]. We characterized
Rgs16 mRNA
expression in C57BL/6 female mice over the first 4 days of
RF (Fig. 4). As
expected, Rgs16 was expressed in liver of fasted mice and
declined to basal
levels by the end of the 4 hr feeding period (ZT5-ZT9).
Restricted feeding
advances and intensifies Rgs16 expression in liver by the
second or third
day of RF (Fig. 4), coincident with increased locomoter
activity as mice
learn to anticipate feeding during the light phase [38].

On the first day of RF, Rgs16 mRNA expression in liver is no
higher at ZT5
than in ad libitum fed mice (see Fig. 1, lane 1, 2), even
though the RF mice
were fasted through the dark phase and had lost 2.5 gm from
their starting
weight (Fig. 4, middle panel). This may reflect an
underlying circadian
regulation of liver gene expression as clock genes show a
similar response
on the first day of RF [35, 36, 38]. During the first 4 hr
feeding period
(day 1), female mice ate about 1.5 gm of chow and regained
about 1 gm body
weight (Fig. 4, bottom panel). However, they ate about half
as much on day 1
as on subsequent days, presumably because they had not yet
learned to
anticipate fasting during the dark phase and feeding during
the light phase.
By day 2 RF, prior to feeding at ZT5, mice lost about 3.5 gm
of their
original weight, but they were alert and active, and ate
voraciously upon
refeeding, consuming about 0.7 gm chow within the first 30
min, 2.5 gm
during 4 hr. This behavior was repeated days 3 and 4 of RF,
and each day
mice regained body weight to within about 1 gm of their
starting weight.

Oscillations in Rgs16 mRNA expression are slightly delayed
in the liver
relative to the SCN in ad libitum fed mice maintained in a
12 hr light-dark
cycle [35, 36, 38]. By contrast, restricted feeding during
the light phase
advances and intensifies Rgs16 expression in liver but does
not alter
expression in SCN (Fig. 4, top panel) presumably reflecting
separate inputs
of nutrients and light regulating Rgs16 expression in liver
and SCN.

Transcriptional control of Rgs16 gene expression
Transcription of the Rgs16
gene is induced during fasting and is inhibited after
feeding. Body weight
and food consumption of male C57BL/6 mice (individually
caged) under RF
conditions is shown (Fig. 5B). On day 3 of RF, fasted males
were sacrificed
at ZT5, or allowed to feed for 20, 40, or 60 min before
sacrifice. Nuclear
run-on assays showed that Rgs16 gene transcription declined
about 5-fold
from fasted levels within 20 min, and was not detectable
above background by
60 min (Fig. 5A).

By contrast, transcription of GAPDH, Rgs8, cyclophilin, and
G?11 remained
essentially constant in liver of fed and fasted mice (Fig.
5A, and data not
shown). Rgs16 mRNA levels declined about 4-fold within the
first 20 min
after refeeding, consistent with the decline in
transcription during the
same interval.

Rgs16 mRNA and protein are rapidly down regulated after
feeding Rgs16 mRNA
and protein expression in liver after a short fast was
somewhat higher in
mice maintained on normal chow compared with a high fat diet
(Fig. 6).
Feeding down regulated both Rgs16 mRNA and protein to basal
levels within
four hours (Figs. 2A, 6A, and data not shown). To compare
the decline in
Rgs16 mRNA and protein levels after feeding, female mice
were fasted from
ZT4 to ZT12; then, provided chow ad libitum at ZT12, and
sacrificed to
collect liver at the indicated times (Fig. 6A). Rgs16 mRNA
and protein
levels declined concomitantly within 20 min after feeding,
falling to nearly
basal levels within 60 min. A rapid decline in Rgs16 mRNA
expression was
also observed when female mice were refed by gavage (1 ml)
of a complete
liquid diet at ZT12 (Fig. 1). In summary, refeeding a
complete chow or
liquid diet down regulates Rgs16 in male and female mice (n
>100) and rats
(n=6).

... By contrast, transcription of GAPDH, Rgs8, cyclophilin,
and G?11
remained essentially constant in liver of fed and fasted
mice (Fig. 5A, and
data not shown). Rgs16 mRNA levels declined about 4-fold
within the first 20
min after refeeding, consistent with the decline in
transcription during the
same interval.

Rgs16 mRNA and protein are rapidly down regulated after
feeding Rgs16 mRNA
and protein expression in liver after a short fast was
somewhat higher in
mice maintained on normal chow compared with a high fat diet
(Fig. 6).
Feeding down regulated both Rgs16 mRNA and protein to basal
levels within
four hours (Figs. 2A, 6A, and data not shown). To compare
the decline in
Rgs16 mRNA and protein levels after feeding, female mice
were fasted from
ZT4 to ZT12; then, provided chow ad libitum at ZT12, and
sacrificed to
collect liver at the indicated times (Fig. 6A). Rgs16 mRNA
and protein
levels declined concomitantly within 20 min after feeding,
falling to nearly
basal levels within 60 min. A rapid decline in Rgs16 mRNA
expression was
also observed when female mice were refed by gavage (1 ml)
of a complete
liquid diet at ZT12 (Fig. 1). In summary, refeeding a
complete chow or
liquid diet down regulates Rgs16 in male and female mice (n
>100) and rats
(n=6). ...

Conclusions
Rgs16 is the only RGS gene (of 20 total) that is diurnally
expressed in
liver of ad libitum fed mice. Restricting feeding entrained
Rgs16
transcription and mRNA expression in liver but did not
affect circadian
regulation of Rgs16 expression in the SCN. Thus, separate
inputs regulate
Rgs16 expression in liver and SCN. Rgs16 gene transcription,
mRNA and
protein levels are rapidly down regulated by feeding. The
expression pattern
and enzymatic activity of Rgs16 identifies it as a candidate
regulator of
Gi/Gq signaling during the transitions from fasting to
feeding in liver and
between light and dark phases in SCN.