MOLECULAR ENDOCRINOLOGY AND IMMUNOLOGY

LECTURE 5/6 - Growth hormone and prolactin

Growth hormone: general actions; structure; evolution; clinical

applications; molecular biology, biosynthesis & secretion

Prolactin: general actions; structure; the cytokine protein family; molecular biology; clinical applications; biosynthesis and secretion

Placental lactogens; primates, rodents ruminants

Evolution of the GH/PRL family: somatolactin

ACROMEGALY

Dwarf mice

Amino acid sequence of bovine growth hormone

AMINO ACID SEQUENCES OF SOME MAMMALIAN GROWTH HORMONES

10 20 30 40 50 60 Pig FPAMPLSSLFANAVLRAQH LHQLAADTYKEFERAYIPEG QRYS-IQNAQAAFCFSETIP Horse ------------------- -------------------- ----•--------------- Dog ------------------- -------------------- ----•--------------- Mole rat -------N----------- -------------------- ----•--------------- Man --TI---R--D--M---HR -----F---Q---E----KE -K--FL--P-TSL----S--

70 80 90 100 110 120Pig APTGKDEAQQRSDVELLRFS LLLIQSWLGPVQFLSRVFTN SLVFGTSD-RVYEKLKDLEEHorse -------------M------ ------------L------- --------•------R----Dog -------------------- -------------------- --------•-----------Mole rat -----E-------M------ -------------------- --------•--F--------Man T-SNRE-T--K-NL----I- --------E-----RS--A- ---Y-A--SN--DL------

130 140 150 160 170 180 Pig GIQALMRELEDGSPRAGQIL KQTYDKFDTNLRSDDALLKN YGLLSCFKKDLHKAETYLRV Horse -------------------- -------------------- -------------------- Dog -------------------- -------------------- -------------------- Mole Rat -------------L----L- ----------M--------- -------------------- Man ---T--GR-------T---F ----S-----SHN------- ----Y--R--MD-V--F--I

190 DIFFSPig MKCRRFVESSCAFHorse ------------- 3Dog ------------- 0Mole Rat ------------- 7Man VQ--•S--G--G- 62

Horse Elephant ManPigAlpacaOxSheep

0

1

18

01

1 5

Goat

0

Dog

0

80

Rat Mouse

2 1

1

7

0

2

Rabbit

7 3

Rhesus

1

0

Hamster0

25

50

75

100

Possum

5

11

0

Red deer

0

3

Whale

4

Rate of evolution

(substitutions/aa site/10 9 yr)

slow phase (excl. rodents) 0.21slow phase (incl. rodents) 0.28rodents 0.49ruminants (rapid phase) 3.8primates (rapid phase) 10.8

Mill

ion

ye

ars

be

fore

pre

sen

t

GROWTH HORMONE EVOLUTION

OVINE GH-RECEPTOR HOMOLOGY MODEL

Alternative splicing of human GH mRNA precursor

0 20 40 6010 30 50

kbp

hGH-N hPL-L hPL-A hGH-V hPL-B

THE HUMAN GROWTH HORMONE GENE CLUSTER

0 20 4010 30 50kbp

hGH-N hPL-L hPL-A hGH-V hPL-B

PRIMATE GROWTH HORMONE GENE CLUSTERS

slGH

Slow loris

Human

Marmoset

1 2 3 4 5 6 7 8

Capuchin ~ 35 'genes'

Pituitary GH Placental expression Expressed? Pseudogene

Transgenic mice

Transgenic mice - growth curves

From: Devlin et al. Nature 371, 209 (1994)

Electron micrograph of a somatotroph

REGULATION OF THE HUMAN GH GENE CLUSTER

From: Ho et al TEM 15, 40-45(2004)

HISTONE ACETYLATION IN THE HUMAN GH GENE CLUSTER

From: Ho et al (2004)

PROLACTIN

Amino acid sequence of bovine prolactin

Comparison of bovine GH and prolactin sequences

COMPARATIVE AND EVOLUTIONARY ASPECTS OF PROLACTIN

• Separate GH and prolactin found in nearly all vertebrates. GH-like molecule in jawless fish (lamprey), but no separate prolactin. No GH-like protein in invertebrates.

• A third GH/prolactin-like pituitary hormone, SOMATOLACTIN, is found in many fish, but not in tetrapods?

• In mammals prolactin shows variable rates of evolution. Human prolactin was identified relatively late - 1970s.

SYNTHESIS AND SECRETION OF PROLACTIN

• “simple precursor”:

sig pept mature prolactin

• single gene in humans

• Synthesized and secreted from lactotrophs, under predominantly negative control from hypothalamus

EXPRESSION OF HUMAN PROLACTIN GENE

From: Ben-Jonathan et al (2002)

CLINICAL ASPECTS OF PROLACTIN

• prolactin-secreting pituitary tumours common. Can cause galactorrhoea and amenorrhoea. Treated with dopamine agonists such as bromocryptine

• possible link to breast cancer??

PLACENTAL LACTOGENS

• In humans placental lactogen (chorionic somatomammotropin) is a GH-like protein, consequent on duplication of the GH gene

• In rodents and ruminants placental lactogens are prolactin-like proteins, resulting from (independent) duplications of the prolactin gene. In both groups there are many (up to 20) prolactin-like genes, in a cluster. Their functions have not yet been fully defined.